Melatonin–Dopamine Crosstalk: A Central Axis in Circadian Regulation and Clinical Chronopharmacology

Ismail Celil Haskologlu

doi:10.33069/cim.2025.0057

Chronobiol Med > Volume 7(4); 2025 > Article

Haskologlu: Melatonin–Dopamine Crosstalk: A Central Axis in Circadian Regulation and Clinical Chronopharmacology

Review Article

Chronobiology in Medicine 2025;7(4):208-216.

Published online: December 31, 2025

DOI: https://doi.org/10.33069/cim.2025.0057

Melatonin–Dopamine Crosstalk: A Central Axis in Circadian Regulation and Clinical Chronopharmacology

Ismail Celil Haskologlu

Department of Pharmacology, Faculty of Pharmacy, Near East University, Nicosia, Cyprus

Corresponding author: Ismail Celil Haskologlu, PhD, Department of Pharmacology, Faculty of Pharmacy, Near East University, 99138 Nicosia, Cyprus.
Tel: 90-0534 554 93 01, E-mail: ismailcelil.haskologlu@neu.edu.tr

Received September 19, 2025 Revised September 26, 2025 Accepted November 18, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Circadian rhythms regulate essential physiological and behavioral functions by aligning them with the environmental light–dark cycle. Melatonin and dopamine are two key neuromodulators that exhibit reciprocal activity patterns and exert opposing effects across the circadian cycle. This review aimed to explore the molecular mechanisms, neurophysiological roles, and clinical relevance of the melatonin–dopamine axis in circadian regulation. A comprehensive analysis of current literature was conducted, focusing on studies describing receptor-mediated signaling and reciprocal regulation of melatonin and dopamine. Emphasis was placed on their functional interactions, as well as their role in the modulation of sleep–wake cycles and circadian entrainment. Clinical studies addressing neurodegenerative and psychiatric disorders were also reviewed to evaluate translational significance. Evidence indicates that melatonin, synthesized during the dark phase, promotes nocturnal physiology and sleep initiation. Conversely, dopamine predominates during the light phase, enhancing arousal, reward processing, and motor activity. Dysregulation of this axis was implicated in Parkinson’s disease, depression, schizophrenia, and addiction. The melatonin–dopamine axis plays a pivotal role in maintaining circadian homeostasis by integrating hormonal and neurotransmitter signals. Targeting this interplay through chronopharmacological interventions holds promise for restoring circadian alignment and improving outcomes in neurological and psychiatric disorders.

Keywords: Melatonin; Dopamine; Circadian rhythm; Sleep–wake cycle; Chronopharmacology

INTRODUCTION

Circadian rhythms are endogenous oscillations with a period of approximately 24 hours that coordinate physiology and behavior with environmental light–dark cycles [1]. These rhythms are orchestrated by a central pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus and are synchronized with peripheral clocks distributed throughout the body. Proper circadian alignment ensures optimal regulation of sleep–wake cycles, hormonal secretion, metabolism, and neuronal signaling [2,3]. Disruption of circadian rhythms was increasingly associated with neurological and psychiatric disorders, highlighting the importance of understanding the molecular interactions that sustain these oscillations [4].

Among the key regulators of circadian physiology, melatonin and dopamine occupy complementary and interconnected roles. Melatonin, a neurohormone synthesized primarily by the pineal gland during the dark phase, conveys information about environmental photoperiods and facilitates nocturnal physiology, including sleep initiation and immune regulation. Acting through its high-affinity receptors MT1 and MT2, melatonin exerts inhibitory effects on intracellular cyclic adenosine monophosphate (cAMP) signaling pathways, thereby modulating neuronal excitability and synchronizing peripheral clocks with the SCN [5].

In contrast, dopamine is a catecholamine neurotransmitter central to the regulation of reward processing, motivation, arousal, and motor control. Dopaminergic activity shows clear diurnal variation, peaking during the light phase when alertness and locomotor activity are required. Dopamine acts through five receptor subtypes (D1–D5) that are differentially expressed across neural circuits, including the striatum, prefrontal cortex, and retina [6].

Mounting evidence suggests that melatonin and dopamine engage in reciprocal regulation. In the retina, melatonin suppresses dopamine release at night to promote rod function and scotopic vision, while dopamine inhibits melatonin signaling during the day to enhance cone-mediated photopic responses [7]. In the central nervous system, melatonin modulates dopaminergic transmission in basal ganglia and hypothalamic pathways, influencing locomotion, reward, and circadian entrainment. Conversely, dopaminergic activity was shown to impact pineal melatonin synthesis, suggesting bidirectional control [8].

The functional consequences of this interaction extend to clinical contexts. Alterations in the melatonin–dopamine axis were implicated in Parkinson’s disease (PD), where dopaminergic degeneration is accompanied by circadian disruption, as well as in psychiatric disorders such as depression, schizophrenia, and attention-deficit/hyperactivity disorder (ADHD). Furthermore, dysregulation of this axis contributes to sleep–wake disturbances, addiction vulnerability, and mood disorders [9].

This review aims to provide a comprehensive overview of the molecular, cellular, and systemic mechanisms underlying the interplay between melatonin and dopamine within circadian regulation. Special emphasis was placed on their reciprocal modulation in the retina and brain, their role in sleep–wake homeostasis, and their implications for neurodegenerative and psychiatric diseases [10]. In addition, emerging therapeutic strategies targeting this axis were discussed, including chronopharmacological approaches designed to optimize treatment outcomes [11].

MOLECULAR AND CELLULAR INTERACTIONS

The molecular interplay between melatonin and dopamine is mediated by their respective receptors, intracellular signaling cascades, and circadian clock components. This bidirectional regulation ensures that the activity of each neuromodulator is temporally restricted, thereby maintaining circadian homeostasis [12]. The reciprocal melatonin–dopamine axis plays a key role in circadian regulation, where melatonin inhibits dopamine release at night and dopamine suppresses melatonin synthesis during the day (Figure 1).

Melatonin receptors and dopaminergic modulation

Melatonin exerts its effects primarily through the high-affinity G protein–coupled receptors MT1 and MT2, which are distributed in the SCN, retina, striatum, and several cortical regions. Both receptors are negatively coupled to adenylate cyclase via Gi/o proteins, leading to decreased cAMP levels and reduced protein kinase A (PKA) activity. This inhibition dampens dopaminergic neurotransmission by lowering dopamine release and altering receptor sensitivity. In the retina, activation of MT1 and MT2 receptors suppresses dopamine release during the night, thus shifting visual sensitivity toward rod photoreceptors and enhancing scotopic vision [13].

Dopamine receptors and pineal melatonin regulation

Conversely, dopamine regulates melatonin synthesis in the pineal gland and retina through its receptor subtypes. D1-like receptors (D1 and D5) stimulate adenylate cyclase, increasing cAMP and promoting arylalkylamine N-acetyltransferase (AANAT) activity, the key enzyme in melatonin synthesis. In contrast, D2-like receptors (D2, D3, D4) inhibit adenylate cyclase and reduce melatonin production. This dual regulation ensures fine-tuned control of melatonin secretion in response to dopaminergic tone and environmental lighting [14].

Reciprocal inhibition and circadian feedback loops

The melatonin–dopamine axis is characterized by reciprocal inhibition. Melatonin signaling decreases dopamine release in dopaminergic terminals, while dopamine can inhibit pineal melatonin output. Such antagonistic interactions create a feedback loop that stabilizes circadian oscillations. Notably, this interplay integrates with the transcription–translation feedback loops (TTFLs) of clock genes. For instance, melatonin influences PER and BMAL1 expression, while dopamine was shown to modulate CLOCK and PER2 activity. These interactions place melatonin and dopamine as modulators of molecular clock machinery beyond their neurotransmitter roles [15].

Intracellular signaling pathways

Both systems converge on common intracellular cascades. Melatonin reduces cAMP and downstream PKA activity, which can suppress dopamine-mediated signaling. Additionally, melatonin activates mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase/Akt (PI3K/Akt) pathways, leading to cytoprotective effects that may counterbalance dopamine-induced oxidative stress. Dopamine, in turn, activates cAMP-response element-binding protein (CREB)-dependent transcription through cAMP, which may influence circadian gene expression. Cross-talk at this intracellular level provides a mechanistic basis for the reciprocal regulation observed at the systems level [16].

FUNCTIONAL IMPLICATIONS OF MOLECULAR INTERACTIONS

The temporal alternation between melatonin and dopamine activities serves as a biological switch between nocturnal and diurnal states. At night, melatonin dominance promotes rest, metabolic conservation, and enhanced dark adaptation. During the day, dopamine dominance supports wakefulness, reward processing, and visual acuity. Disruption of this molecular balance—for example, by chronic stress, neurodegeneration, or artificial light exposure—can desynchronize circadian rhythms and contribute to disease pathology [17]. These molecular dynamics are summarized in Table 1, which outlines the principal receptors, signaling pathways, dominant circadian phases, and reciprocal inhibitory effects of melatonin and dopamine across key anatomical sites.

Retinal and visual system crosstalk

The retina provides one of the most well-characterized models of melatonin–dopamine interaction within the circadian system. Retinal circuits rely on a finely tuned balance between these two neuromodulators to regulate visual sensitivity across the light–dark cycle. Their reciprocal regulation ensures that photoreceptor and interneuron activity are appropriately adapted to day and night conditions [18].

Melatonin is synthesized locally in the retina by photoreceptors, primarily during the night. Its release follows a robust circadian pattern controlled by intrinsic clock gene expression and pineal-derived cues. Melatonin receptors, particularly MT1 and MT2, are expressed in photoreceptor cells, retinal ganglion cells, and horizontal cells [19]. Activation of these receptors during darkness reduces dopamine release, thereby promoting rod-dominated visual processing. This mechanism enhances scotopic vision, increases sensitivity to low light, and suppresses cone-mediated photopic function, aligning visual performance with nocturnal conditions [20].

Dopamine, in contrast, is synthesized by a subset of amacrine cells and is predominantly released during the daytime. Its circadian secretion pattern is strongly light-dependent, peaking under photopic conditions. Dopamine acts through D1-like and D2-like receptors distributed across bipolar, horizontal, and amacrine cells, where it modulates gap junction coupling, photoreceptor activity, and neurotransmitter release [21]. Functionally, dopamine promotes cone dominance, increases contrast sensitivity, and enhances visual acuity under bright light conditions.

Reciprocal inhibition and photoreceptor adaptation

Melatonin and dopamine act as functional antagonists in retinal physiology. Nocturnal melatonin secretion inhibits dopamine release, thus reducing cone activity and facilitating rod-driven responses. Conversely, dopamine released during the day suppresses melatonin synthesis, reinforcing cone-mediated vision and dampening rod sensitivity. This reciprocal inhibition provides a molecular switch that aligns retinal function with environmental light levels [22].

Retinal clock and circadian entrainment

The retina contains an intrinsic circadian oscillator independent of the SCN, which regulates melatonin and dopamine release. Clock genes such as PER1, PER2, and BMAL1 show circadian oscillations in retinal cells and interact with melatonin–dopamine signaling. Through this mechanism, the retina not only adapts to daily light–dark changes but also provides photic input to the SCN via intrinsically photosensitive retinal ganglion cells (ipRGCs). Thus, melatonin–dopamine crosstalk within the retina contributes both to local visual adaptation and systemic circadian entrainment [23].

PATHOPHYSIOLOGICAL IMPLICATIONS

Disturbances in the melatonin–dopamine balance in the retina were linked to visual dysfunctions and circadian disruption. For example, reduced melatonin secretion in aging or neurodegenerative disease may impair night vision and alter dopaminergic regulation, contributing to sleep–wake disturbances. Conversely, excessive dopamine signaling was implicated in retinal degeneration and light-induced damage. These findings highlight the retina as a critical site where circadian and neurotransmitter systems intersect, with implications extending beyond vision to systemic health [24].

Central nervous system crosstalk

Beyond the retina, the interplay between melatonin and dopamine extends to central brain structures that regulate circadian rhythms, arousal, and reward-related behaviors. This crosstalk is particularly evident in the SCN, the striatum and basal ganglia, and the sleep–wake regulatory networks, where reciprocal modulation shapes neural activity across the 24-hour cycle [25].

The suprachiasmatic nucleus

The SCN acts as the master circadian pacemaker, synchronizing peripheral clocks and coordinating daily behavioral rhythms. Dopaminergic input to the SCN is relatively modest compared to other brain regions, yet it influences light-induced phase shifts and clock gene expression. Dopamine signaling, particularly through D1 receptors, can alter the expression of PER1 and PER2, thereby modulating circadian phase. Conversely, melatonin exerts inhibitory actions on SCN neurons via MT1 receptors, reducing neuronal firing during the night and consolidating nocturnal rest. Through this mechanism, melatonin dampens dopaminergic activation in the SCN, while dopamine can fine-tune photic entrainment of circadian rhythms [26].

Striatum and basal ganglia

The striatum is a major dopaminergic hub where circadian modulation plays a central role in motor control and reward processing. Dopamine release in the striatum follows a robust diurnal pattern, peaking during the active phase [27]. Melatonin receptors (MT1/MT2) expressed in striatal neurons can inhibit dopaminergic signaling, reducing locomotor activity at night. Experimental studies have shown that melatonin administration decreases dopamine turnover in the striatum and substantia nigra, suggesting a suppressive influence on basal ganglia circuits. This reciprocal regulation links circadian timing to dopaminergic control of movement and motivation, providing a mechanistic basis for daily fluctuations in motor performance and reward sensitivity [28].

Sleep–wake regulation

The balance between melatonin and dopamine is critical for sleep–wake homeostasis. Melatonin promotes sleep initiation by reducing SCN activity and enhancing parasympathetic tone, while dopamine facilitates arousal and vigilance through mesocorticolimbic and nigrostriatal pathways. Dopaminergic neurons in the ventral tegmental area (VTA) and substantia nigra exhibit circadian oscillations in activity, aligning wakefulness with the light phase. Excessive dopamine signaling is associated with insomnia and fragmented sleep, whereas elevated melatonin secretion improves sleep onset and continuity. Thus, circadian alternation between melatonin and dopamine dominance orchestrates the timing of sleep and wake states [29].

Integration with clock gene networks

Both melatonin and dopamine interact with the molecular circadian machinery at the transcriptional level. Melatonin influences the expression of BMAL1 and PER genes, while dopamine modulates CLOCK and PER2 transcription via CREB-dependent pathways. This dual regulation integrates neurotransmitter activity with the TTFLs that underlie circadian oscillations [30]. Such interactions ensure that dopaminergic activity peaks during the subjective day, while melatonin secretion dominates during the night.

CLINICAL IMPLICATIONS OF CENTRAL CROSSTALK

Dysregulation of central melatonin–dopamine interactions was implicated in a range of disorders. In PD, degeneration of dopaminergic neurons in the substantia nigra is accompanied by circadian and sleep disturbances, partly due to altered melatonin rhythms. In psychiatric conditions such as schizophrenia and bipolar disorder, disrupted dopamine transmission coincides with abnormal melatonin secretion, contributing to circadian disruption and mood instability [31]. Understanding these central interactions provides a framework for therapeutic strategies that combine dopaminergic agents with melatonin-based interventions to restore circadian balance.

Clinical implications

The reciprocal regulation of melatonin and dopamine is not only a fundamental feature of circadian physiology but also a critical factor in the pathogenesis of several neurological and psychiatric conditions. Dysregulation of this axis contributes to neurodegeneration, mood instability, sleep disorders, and altered reward processing [32]. The clinical relevance of melatonin–dopamine crosstalk across neurological and psychiatric disorders is summarized in Table 2, which highlights typical circadian alterations, dopaminergic and melatonergic changes, associated clinical outcomes, and potential therapeutic strategies.

Parkinson’s disease

PD is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta, leading to motor dysfunction and common non-motor symptoms such as sleep and circadian disturbances. Patients with PD often show reduced amplitude and altered timing of melatonin secretion, paralleling dopaminergic deficits. Melatonin was shown to exert neuroprotective and antioxidant effects, potentially mitigating oxidative stress and mitochondrial dysfunction that exacerbate dopaminergic cell loss [33].

At the same time, dopaminergic medications such as levodopa or dopamine agonists may disrupt circadian rhythms and suppress endogenous melatonin secretion, leading to insomnia and excessive daytime sleepiness. Clinical studies suggest that melatonin supplementation improves subjective sleep quality in PD patients, though its efficacy for motor symptoms remains inconclusive. Targeting the melatonin–dopamine axis may therefore provide a dual therapeutic avenue: preserving dopaminergic function while stabilizing circadian rhythms [34].

Psychiatric disorders

Depression is a major depressive disorder associated with circadian disruption, reduced nocturnal melatonin secretion, and hyperactivity of dopaminergic reward circuits. Melatonin dysregulation may contribute to sleep disturbances and impaired mood regulation. Agomelatine, a melatonin receptor agonist and serotonin receptor antagonist, demonstrates antidepressant efficacy by restoring circadian rhythms and indirectly modulating dopamine activity in the prefrontal cortex [35].

Schizophrenia is characterized by altered dopaminergic neurotransmission, with mesolimbic hyperdopaminergia and cortical hypodopaminergia. These disturbances may worsen cognitive and affective symptoms and contribute to antipsychotic-induced insomnia. Patients also show abnormal melatonin secretion patterns and fragmented circadian rhythms [36]. Adjunctive melatonin therapy was reported to improve sleep quality and reduce oxidative stress in schizophrenia, though its impact on psychotic symptoms remains limited [37].

ADHD is characterized by dopaminergic dysregulation in fronto-striatal networks and frequent circadian rhythm disturbances, including delayed sleep phase syndrome. Melatonin treatment was effective in improving sleep onset latency and circadian alignment in children and adults with ADHD, suggesting that melatonin–dopamine interactions may underlie both sleep and attentional symptoms [38].

Addiction and reward dysregulation

The dopaminergic mesolimbic pathway, particularly projections from the VTA to the nucleus accumbens, is central to reward processing and drug reinforcement. Circadian disruption enhances vulnerability to addictive behaviors, partly by altering melatonin–dopamine dynamics [39].

Melatonin was shown to attenuate drug-seeking behaviors in animal models of cocaine, methamphetamine, and alcohol dependence, potentially through inhibition of dopamine release and modulation of oxidative stress. Conversely, chronic drug use disrupts melatonin secretion and circadian rhythms, creating a vicious cycle of reward dysregulation and sleep impairment. Chronotherapeutic interventions that restore melatonin signaling may therefore reduce relapse risk and stabilize reward circuitry [40].

Sleep disorders and circadian disruption

Sleep–wake disturbances are frequently linked to imbalances in melatonin and dopamine activity. Excessive dopaminergic tone, such as in restless legs syndrome or stimulant use, leads to insomnia, while insufficient dopamine may contribute to hypersomnia [41]. Melatonin supplementation, by contrast, improves sleep initiation and circadian alignment, particularly in shift work disorder, jet lag, and delayed sleep phase syndrome. The dynamic balance between melatonin’s sleep-promoting effects and dopamine’s arousal-promoting actions is thus fundamental to sleep homeostasis [42].

Broader neurological and metabolic disorders

Beyond neurodegeneration and psychiatry, dysregulation of melatonin–dopamine interactions was implicated in metabolic syndrome, Alzheimer’s disease, and seasonal affective disorder. In these conditions, circadian disruption and dopaminergic imbalance exacerbate clinical symptoms, and targeting the melatonin–dopamine axis may represent a novel therapeutic approach [43].

THERAPEUTIC PERSPECTIVES

The circadian crosstalk between melatonin and dopamine has opened new avenues for pharmacological and chronotherapeutic interventions, with the ultimate goal of restoring circadian alignment, improving sleep–wake regulation, and alleviating neuropsychiatric symptoms. Several therapeutic strategies were developed to target this axis, ranging from melatonin supplementation and synthetic analogues to dopaminergic agents and time-specific treatment approaches [44].

Melatonin itself remains one of the most widely used agents in clinical practice for circadian rhythm disorders, insomnia, and jet lag [45]. In patients with dopaminergic dysfunction, such as those with PD or schizophrenia, melatonin administration was shown to improve sleep quality and reduce oxidative stress, although its effects on motor or cognitive outcomes are more variable. Beyond endogenous melatonin, synthetic receptor agonists with improved pharmacokinetic properties have expanded the therapeutic potential of this pathway. Agomelatine, for instance, combines MT1 and MT2 receptor agonism with 5-HT2C antagonism, resulting in enhanced dopamine and norepinephrine release in the prefrontal cortex while simultaneously restoring circadian alignment. It is currently approved as an antidepressant and represents one of the best examples of melatonin–dopamine interplay being harnessed clinically [46]. Similarly, ramelteon, a selective MT1/MT2 agonist, has proven effective for insomnia by stabilizing circadian rhythms without dopaminergic side effects, while tasimelteon has demonstrated efficacy in entraining circadian rhythms in patients with non-24-hour sleep–wake disorder, particularly in blind individuals [47].

Dopaminergic agents themselves also have significant circadian implications. In PD, dopamine replacement therapy with levodopa or dopamine agonists improves motor function but can exacerbate circadian disruption by suppressing melatonin secretion and altering sleep architecture. Such agents are frequently associated with insomnia, fragmented sleep, and excessive daytime somnolence. Conversely, dopamine antagonists employed in psychiatric disorders, such as antipsychotics, may counteract hyperdopaminergic states but at the expense of circadian stability and metabolic balance. This duality highlights the need for careful consideration of not only drug choice but also the timing of administration in order to optimize both therapeutic efficacy and circadian homeostasis [48].

Chronopharmacology provides an important framework for refining these approaches. By administering medications in alignment with biological rhythms, it is possible to maximize drug efficacy and minimize adverse effects [49]. Evening melatonin or melatonergic agonists, for example, enhance sleep initiation and circadian synchronization, while morning dopaminergic therapy in PD is more effective for motor control and less disruptive to nocturnal physiology. Chronobiotic antidepressants such as agomelatine demonstrate the value of this approach by simultaneously improving mood and reinforcing circadian organization. The growing field of personalized chronotherapy further emphasizes the importance of tailoring treatments to individual chronotype, genetic variation in clock or dopamine receptor genes, and sleep–wake patterns [50].

There is also increasing interest in combination therapies that modulate both melatonergic and dopaminergic signaling simultaneously. Melatonin supplementation alongside dopaminergic therapy in PD, for instance, may mitigate sleep disturbances without reducing the motor benefits of dopamine replacement [51]. Similarly, agomelatine’s dual action on melatonin and serotonin receptors indirectly enhances dopaminergic transmission, producing robust antidepressant effects. Looking ahead, the development of dual-target ligands or multidrug regimens designed to balance melatonin and dopamine activity may offer new solutions for disorders ranging from insomnia and mood dysregulation to neurodegeneration [52].

Future perspectives extend beyond classical pharmacology. Advances in gene therapy, nanoparticle-based delivery systems, and the integration of light therapy with melatonin agonists highlight the translational potential of this field. Equally important are lifestyle-based interventions, such as sleep hygiene, diet, and timed exercise, which can complement pharmacological treatments and reinforce circadian stability [53-56]. Table 3 summarizes the major therapeutic strategies targeting the melatonin–dopamine axis, outlining pharmacological agents, their molecular targets, optimal timing of administration, expected circadian and sleep effects, and relevant clinical notes.

CONCLUSION AND FUTURE DIRECTIONS

The interaction between melatonin and dopamine represents a fundamental aspect of circadian physiology, integrating hormonal and neurotransmitter signals to regulate daily rhythms of sleep, arousal, vision, and behavior. This reciprocal relationship ensures that melatonin dominates during the dark phase, promoting rest and nocturnal physiology, while dopamine predominates during the light phase, facilitating alertness, reward processing, and motor activity. At the molecular level, this crosstalk is mediated through melatonin and dopamine receptors, intracellular signaling cascades, and clock gene networks, with particularly robust effects observed in the retina, the SCN, and dopaminergic circuits of the basal ganglia. By stabilizing circadian oscillations and aligning neuronal function with environmental light–dark cycles, the melatonin–dopamine axis emerges as a central regulator of both physiological adaptation and neurological health.

Disruptions of this finely balanced system were increasingly linked to the pathophysiology of a wide range of disorders, including PD, schizophrenia, depression, and substance use disorders, as well as sleep–wake disturbances and age-related circadian disruption. In each case, dysregulation of melatonin secretion, dopaminergic signaling, or their reciprocal interactions contributes to clinical symptoms and disease progression. These observations not only highlight the importance of the melatonin–dopamine axis in maintaining circadian homeostasis but also suggest that it may serve as a therapeutic target across multiple domains of neurology and psychiatry.

Therapeutic strategies that address this axis are already in clinical use, with melatonin supplementation and synthetic analogues improving sleep quality and circadian entrainment, and melatonergic antidepressants such as agomelatine demonstrating efficacy through combined circadian and dopaminergic modulation. At the same time, dopaminergic agents used in PD and psychiatric disorders continue to reveal both the potential benefits and circadian challenges of targeting this system. Chronopharmacological approaches that optimize the timing of these treatments are emerging as particularly promising, as they allow interventions to align more closely with endogenous biological rhythms.

Looking forward, future research must further clarify the molecular mechanisms underlying melatonin–dopamine crosstalk, particularly their integration with core clock gene networks and intracellular signaling pathways. Translational studies are needed to determine how these mechanisms can be leveraged for therapeutic benefit, with an emphasis on personalized medicine approaches that consider individual chronotype, genetic background, and lifestyle factors.

Future research should also address how genetic polymorphisms in melatonin and dopamine receptors (e.g., MTNR1B, DRD2, and CLOCK variants) influence individual circadian profiles and treatment responses. Integrating chronotype-specific therapy and genetic screening could refine personalized chronopharmacology. Additionally, combining wearable circadian monitoring with AI-based modeling may facilitate individualized therapeutic timing.

Novel interventions, including dual-target ligands, advanced drug delivery systems, gene therapy, and combinations of pharmacological and behavioral chronotherapy, hold considerable promise. Moreover, the integration of light-based therapies and lifestyle modifications with pharmacological strategies may offer a holistic framework for restoring circadian balance.

In conclusion, the melatonin–dopamine axis represents a vital intersection between circadian biology and neurochemical regulation, with profound implications for health and disease. By deepening our understanding of this interplay and advancing therapeutic strategies that harness its potential, it may be possible to not only alleviate symptoms of neurodegenerative and psychiatric disorders but also to restore the fundamental rhythms that sustain human physiology.

NOTES

Conflicts of Interest

The author has no potential conflicts of interest to disclose.

Availability of Data and Material

Data sharing not applicable to this article as no datasets were generated or analyzed during the study.

Funding Statement

None

Acknowledgments

None

Figure 1.

The melatonin–dopamine axis in circadian regulation. The bidirectional interactions between melatonin and dopamine across the circadian cycle. During the dark phase, melatonin binds to MT1 and MT2 receptors in the suprachiasmatic nucleus (SCN), retina, and striatum, reducing intracellular cyclic AMP (cAMP) and protein kinase A (PKA) activity, thereby suppressing dopamine release. During the light phase, dopamine released from ventral tegmental area (VTA) and retinal amacrine cells activates D1–D5 receptors, increasing cAMP and cAMP-response element-binding protein (CREB)-dependent transcription, which in turn inhibits melatonin synthesis. ADHD, attention-deficit/hyperactivity disorder.

Table 1.

Functional interplay between melatonin and dopamine systems

System	Main receptors	Key signaling pathways	Effect on the opposing system	Dominant phase	Principal anatomical sites
Melatonin	MT1, MT2	↓cAMP/PKA via Gi/o; MAPK/ERK, PI3K/Akt activation	Inhibits dopamine release and receptor sensitivity	Night	Retina (photoreceptors, RGCs), SCN, striatum
Dopamine	D1–D5 (D1-like: D1/D5; D2-like: D2/D3/D4)	D1-like: ↑cAMP/PKA/CREB; D2-like: ↓cAMP	Suppresses melatonin synthesis and signaling	Day	Retina (amacrine cells), striatum, VTA/SN, hypothalamus

MT1/MT2, melatonin receptor subtypes 1 and 2; D1–D5, dopamine receptor subtypes 1 to 5; SCN, suprachiasmatic nucleus; VTA, ventral tegmental area; SN, substantia nigra; cAMP, cyclic adenosine monophosphate; PKA, protein kinase A; CREB, cAMP-response element-binding protein; MAPK/ERK, mitogen-activated protein kinase/extracellular signal-regulated kinase; PI3K/Akt, phosphatidylinositol 3-kinase/Akt pathway; RGC, retinal ganglion cell.

Table 2.

Clinical implications of melatonin–dopamine dysregulation

Disorder group	Typical circadian findings	Dopamine status	Melatonin status	Clinical outcome	Potential therapeutic approach
Parkinson’s disease	Sleep disturbances, phase shifts	↓Nigrostriatal dopamine	Reduced amplitude, altered timing	Motor + non-motor worsening	Evening melatonin/ramelteon; morning dopaminergic therapy; time-adjusted dosing
Depression	Circadian misalignment, altered chronotype	Mesocortical hypodopaminergia	Decreased/nocturnal irregularity	Anhedonia, insomnia	Agomelatine; light therapy; chronotherapy
Schizophrenia	Fragmented rhythms, insomnia	↑Mesolimbic, ↓cortical	Abnormal secretion pattern	Cognitive + affective instability	Antipsychotic timing + adjunctive melatonin
ADHD	Delayed sleep phase	Fronto-striatal dysregulation	Delayed onset	Sleep initiation problems, inattention	Melatonin at night; stimulants in the morning
Addiction	Disrupted circadian rhythms	Mesolimbic hyperreactivity	Irregular rhythm	Relapse risk, reward dysregulation	Melatonin + sleep hygiene/light therapy
Sleep disorders	Jet lag, shift work, DSPS	Various	Various	Insomnia, hypersomnia	Timed melatonin/tasimelteon

ADHD, attention-deficit/hyperactivity disorder; DSPS, delayed sleep phase syndrome.

Table 3.

Therapeutic strategies modulating the melatonin–dopamine axis

Agent	Target	Optimal timing	Expected circadian effect	Sleep effect	Notes
Melatonin	MT1/MT2	Evening (1–2 h before bedtime)	Phase advance, circadian entrainment	Improves sleep onset	Safe, antioxidant
Ramelteon	MT1/MT2 agonist	Evening	SCN suppression at night	Improves initiation	No dopaminergic side effects
Tasimelteon	MT1/MT2 agonist	Evening	Entrainment in non-24 rhythms	Aligns sleep–wake	Strong evidence in blind patients
Agomelatine	MT1/MT2 agonist + 5-HT2C antagonist	Evening	Circadian stabilization, ↑prefrontal dopamine	Sleep + mood benefits	Antidepressant; monitor liver function
Levodopa/Dopamine agonists	D1/D2 pathways	Morning/early day	Minimizes nocturnal melatonin suppression	Improves motor function, may fragment sleep	Dose timing critical
Antipsychotics	D2 antagonists	Evening (sedative agents)	May disrupt circadian stability, ↑metabolic risk	Sedation, altered architecture	Adjunctive melatonin may help

MT1/MT2, melatonin receptor subtypes 1 and 2; 5-HT2C, serotonin receptor 2C; D1/D2, dopamine receptor subtypes 1 and 2; SCN, suprachiasmatic nucleus.

REFERENCES

1. Erdag E. A new tick on the clock: indole-based optimization of melatonin receptor modulators. Chronobiol Med 2025;7:88–94.

2. Thakur A, Kishore R. Neurobiology of the circadian clock and its role in cardiovascular disease: mechanisms, biomarkers, and chronotherapy. Neurobiol Sleep Circadian Rhythms 2025;19:100131.

3. Ozverel CS, Erdag E. Enhancing quality of life in multiple sclerosis patients through coadministration of FDA-approved immunomodulators and melatonin. Chronobiol Med 2024;6:135–142.

4. Baser KHC, Haskologlu IC, Erdag E. Molecular links between circadian rhythm disruption, melatonin, and neurodegenerative diseases: an updated review. Molecules 2025;30:1888.

5. Comai S, Gobbi G. Melatonin, melatonin receptors and sleep: moving beyond traditional views. J Pineal Res 2024;76:e13011.

6. Erdag E, Haskologlu IC. Microglial neuroinflammation in Alzheimer’s disease: mechanisms and therapies. J Dement Alzheimer's Dis 2025;2:29.

7. Aykan U, Güvel MC, Paykal G, Uluoglu C. Neuropharmacologic modulation of the melatonergic system. Explor Neurosci 2023;2:287–306.

8. Horodincu L, Solcan C. Influence of different light spectra on melatonin synthesis by the pineal gland and influence on the immune system in chickens. Animals (Basel) 2023;13:2095.

9. Asadpoordezaki Z, Coogan AN, Henley BM. Chronobiology of Parkinson’s disease: past, present and future. Eur J Neurosci 2023;57:178–200.

10. Que M, Li Y, Wang X, Zhan G, Luo X, Zhou Z. Role of astrocytes in sleep deprivation: accomplices, resisters, or bystanders? Front Cell Neurosci 2023;17:1188306.

11. Kaşkal M, Sevim M, Ülker G, Keleş C, Bebitoğlu BT. The clinical impact of chronopharmacology on current medicine. Naunyn Schmiedebergs Arch Pharmacol 2025;398:6179–6191.

12. Kim P, Oster H, Lehnert H, Schmid SM, Salamat N, Barclay JL, et al. Coupling the circadian clock to homeostasis: the role of period in timing physiology. Endocr Rev 2019;40:66–95.

13. Boczek T, Mackiewicz J, Sobolczyk M, Wawrzyniak J, Lisek M, Ferenc B, et al. The role of G protein-coupled receptors (GPCRs) and calcium signaling in schizophrenia. Focus on GPCRs activated by neurotransmitters and chemokines. Cells 2021;10:1228.

14. Pundkar C, Thanapaul RJRS, Govindarajulu M, Phuyal G, Long JB, Arun P. Dysregulation of retinal melatonin biosynthetic pathway and differential expression of retina-specific genes following blast-induced ocular injury in ferrets. Neurol Int 2025;17:42.

15. Pe LS, Pe KCS, Panmanee J, Govitrapong P, Yang JL, Mukda S. Plausible therapeutic effects of melatonin and analogs in the dopamine-associated pathophysiology of bipolar disorder. J Psychiatr Res 2025;182:13–20.

16. Maity S, Guchhait R, Pramanick K. Melatonin mediated activation of MAP kinase pathway may reduce DNA damage stress in plants: a review. Biofactors 2022;48:965–971.

17. Montaruli A, Castelli L, Mulè A, Scurati R, Esposito F, Galasso L, et al. Biological rhythm and chronotype: new perspectives in health. Biomolecules 2021;11:487.

18. Kinane C, Calligaro H, Jandot A, Coutanson C, Haddjeri N, Bennis M, et al. Dopamine modulates the retinal clock through melanopsin-dependent regulation of cholinergic waves during development. BMC Biol 2023;21:146.

19. Felder-Schmittbuhl MP, Hicks D, Ribelayga CP, Tosini G. Melatonin in the mammalian retina: synthesis, mechanisms of action and neuroprotection. J Pineal Res 2024;76:e12951.

20. Elul D, McKyton A, Levin N. Temporal sensitivity under photopic and scotopic conditions across the cortical visual hierarchy. Invest Ophthalmol Vis Sci 2025;66:12.

21. Lam DM, Ayoub G. Retinal neurochemistry. Brain Sci 2025;15:727.

22. Tosini G, Dirden JC. Dopamine inhibits melatonin release in the mammalian retina: in vitro evidence. Neurosci Lett 2000;286:119–122.

23. Bhoi JD, Goel M, Ribelayga CP, Mangel SC. Circadian clock organization in the retina: from clock components to rod and cone pathways and visual function. Prog Retin Eye Res 2023;94:101119.

24. Haskologlu IC, Erdag E, Sehirli AO, Uludag O, Abacioglu N. Beyond conventional therapies: molecular dynamics of Alzheimer's treatment through CLOCK/BMAL1 interactions. Curr Alzheimer Res 2024;20:862–874.

25. Erdag E, Haskologlu IC, Mercan M, Abacioglu N, Sehirli AO. An in silico investigation: can melatonin serve as an adjuvant in NR1D1-linked chronotherapy for amyotrophic lateral sclerosis? Chronobiol Int 2023;40:1395–1403.

26. Porcu A, Riddle M, Dulcis D, Welsh DK. Photoperiod-induced neuroplasticity in the circadian system. Neural Plast 2018;2018:5147585.

27. Stowe TA, Pitts EG, Leach AC, Iacino MC, Niere F, Graul B, et al. Diurnal rhythms in cholinergic modulation of rapid dopamine signals and associative learning in the striatum. Cell Rep 2022;39:110633.

28. Benleulmi-Chaachoua A, Hegron A, Le Boulch M, Karamitri A, Wierzbicka M, Wong V, et al. Melatonin receptors limit dopamine reuptake by regulating dopamine transporter cell-surface exposure. Cell Mol Life Sci 2018;75:4357–4370.

29. Holst SC, Landolt HP. Sleep-wake neurochemistry. Sleep Med Clin 2018;13:137–146.

30. Fagiani F, Baronchelli E, Pittaluga A, Pedrini E, Scacchi C, Govoni S, et al. The circadian molecular machinery in CNS cells: a fine tuner of neuronal and glial activity with space/time resolution. Front Mol Neurosci 2022;15:937174.

31. Yalçin M, Grande V, Outeiro TF, Relógio A. Circadian clock dysfunction in Parkinson's disease: mechanisms, consequences, and therapeutic strategy. NPJ Parkinsons Dis 2025;11:213.

32. Codoñer-Franch P, Gombert M, Martínez-Raga J, Cenit MC. Circadian disruption and mental health: the chronotherapeutic potential of microbiome-based and dietary strategies. Int J Mol Sci 2023;24:7579.

33. Erdag E. Molecular and mathematical models in Parkinson’s and Alzheimer’s diseases: optimizing the timing of drugs. Chem Methodol 2024;8:569–584.

34. Zuzuárregui JRP, During EH. Sleep issues in Parkinson's disease and their management. Neurotherapeutics 2020;17:1480–1494.

35. Hu X, Zhang A, Wang C, Zhang X. Melatonin rhythm disorder is more pronounced in major depressive disorder with non-suicidal self-injury. Front Neurosci 2025;19:1534715.

36. Morera-Fumero AL, Abreu-Gonzalez P. Role of melatonin in schizophrenia. Int J Mol Sci 2013;14:9037–9050.

37. Moon E, Kim K, Partonen T, Linnaranta O. Role of melatonin in the management of sleep and circadian disorders in the context of psychiatric illness. Curr Psychiatry Rep 2022;24:623–634.

38. van Andel E, Bijlenga D, Vogel SWN, Beekman ATF, Kooij JJS. Effects of chronotherapy on circadian rhythm and ADHD symptoms in adults with attention-deficit/hyperactivity disorder and delayed sleep phase syndrome: a randomized clinical trial. Chronobiol Int 2021;38:260–269.

39. Becker-Krail DD, Walker WH 2nd, Nelson RJ. The ventral tegmental area and nucleus accumbens as circadian oscillators: implications for drug abuse and substance use disorders. Front Physiol 2022;13:886704.

40. Onaolapo OJ, Onaolapo AY. Melatonin in drug addiction and addiction management: exploring an evolving multidimensional relationship. World J Psychiatry 2018;8:64–74.

41. Duan X, Liu H, Hu X, Yu Q, Kuang G, Liu L, et al. Insomnia in Parkinson’s disease: causes, consequences, and therapeutic approaches. Mol Neurobiol 2025;62:2292–2313.

42. Tóth A, Dobolyi Á. Prolactin in sleep and EEG regulation: new mechanisms and sleep-related brain targets complement classical data. Neurosci Biobehav Rev 2025;169:106000.

43. Giannotta G, Ruggiero M, Trabacca A. Chronobiology in paediatric neurological and neuropsychiatric disorders: harmonizing care with biological clocks. J Clin Med 2024;13:7737.

44. Zisapel N. Melatonin-dopamine interactions: from basic neurochemistry to a clinical setting. Cell Mol Neurobiol 2001;21:605–616.

45. Zisapel N. New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation. Br J Pharmacol 2018;175:3190–3199.

46. Kołodziejska R, Woźniak A, Bilski R, Wesołowski R, Kupczyk D, Porzych M, et al. Melatonin—a powerful antioxidant in neurodegenerative diseases. Antioxidants (Basel) 2025;14:819.

47. Kim HK, Yang KI. Melatonin and melatonergic drugs in sleep disorders. Transl Clin Pharmacol 2022;30:163–171.

48. Scanga A, Lafontaine AL, Kaminska M. An overview of the effects of levodopa and dopaminergic agonists on sleep disorders in Parkinson’s disease. J Clin Sleep Med 2023;19:1133–1144.

49. Colita CI, Hermann DM, Filfan M, Colita D, Doepnner TR, Tica O, et al. Optimizing chronotherapy in psychiatric care: the impact of circadian rhythms on medication timing and efficacy. Clocks Sleep 2024;6:635–655.

50. Noguchi Y, Masuda R, Aizawa H, Yoshimura T. Relationship between melatonin receptor agonists and Parkinson’s disease. J Pineal Res 2024;76:e13002.

51. Asemi-Rad A, Moafi M, Aliaghaei A, Abbaszadeh HA, Abdollahifar MA, Ebrahimi MJ, et al. The effect of dopaminergic neuron transplantation and melatonin co-administration on oxidative stress-induced cell death in Parkinson’s disease. Metab Brain Dis 2022;37:2677–2685.

52. Guardiola-Lemaitre B, De Bodinat C, Delagrange P, Millan MJ, Munoz C, Mocaër E. Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties. Br J Pharmacol 2014;171:3604–3619.

53. Liu H, Wang S, Wang J, Guo X, Song Y, Fu K, et al. Energy metabolism in health and diseases. Signal Transduct Target Ther 2025;10:69.

54. Núñez-Cortés R, Salazar-Méndez J, Nijs J. Physical activity as a central pillar of lifestyle modification in the management of chronic musculoskeletal pain: a narrative review. J Funct Morphol Kinesiol 2025;10:183.

55. Na JH, Jeon H, Shim JE, Lee H, Lee YM. Effectiveness and safety of CGRP-targeted therapies combined with lifestyle modifications for chronic migraine in Korean pediatric patients: a retrospective study. Brain Sci 2025;15:493.

56. Haskologlu IC, Erdag E, Uludag O. Can piperazine-bearing fluoro-benzoxazolone derivatives be a chronotherapeutic solution for pain management? Chronobiol Med 2025;7:154–161.