Red Light Therapy for Serotonin & Dopamine

The relationship between light and brain chemistry is one of the most well-established connections in neuroscience. Seasonal affective disorder, circadian rhythm disruption, and the mood-boosting effects of natural sunlight all demonstrate that light exposure directly influences neurotransmitter production. Red light therapy — specifically photobiomodulation (PBM) — extends this relationship into wavelengths beyond the visible spectrum, with emerging evidence suggesting effects on serotonin, dopamine, and melatonin through mechanisms distinct from ordinary daylight exposure.

This page examines what the evidence actually shows about PBM and neurotransmitter production, separating the established science from speculation.

How Light Affects Neurotransmitters: The Established Science

Before discussing red and near-infrared light specifically, it is worth understanding the well-documented pathways through which light influences brain chemistry.

The Retinal Pathway (Blue-Green Light)

The most studied light-brain connection operates through intrinsically photosensitive retinal ganglion cells (ipRGCs) in the eye. These specialised cells contain melanopsin, a photopigment that responds primarily to blue light (460–490 nm). When stimulated, ipRGCs signal the suprachiasmatic nucleus (SCN) — the brain’s master circadian clock — which in turn regulates:

• Melatonin suppression — bright light (particularly blue light) suppresses pineal melatonin production, promoting wakefulness
• Serotonin production — light exposure increases serotonin synthesis in the dorsal raphe nucleus. Lambert et al. (2002) demonstrated that brain serotonin turnover is lowest in winter and highest in summer, directly correlating with daylight hours (The Lancet, 360(9348):1840-1842)
• Cortisol rhythms — morning light exposure helps establish the cortisol awakening response

This retinal pathway is the basis for light therapy boxes used to treat seasonal affective disorder (SAD). It operates through blue-green wavelengths and requires ocular light exposure.

The Non-Retinal Pathway (Red and Near-Infrared)

PBM at red (630–660 nm) and near-infrared (800–850 nm) wavelengths operates through a fundamentally different mechanism. These wavelengths are absorbed by cytochrome c oxidase (CCO) in the mitochondrial electron transport chain, increasing ATP production, modulating reactive oxygen species, and activating downstream signalling cascades.

This is not a circadian signalling pathway. It is a direct cellular energy pathway that can influence neurotransmitter production through metabolic support rather than photic signalling.

PBM and Serotonin

The Biological Rationale

Serotonin (5-hydroxytryptamine, 5-HT) is synthesised from tryptophan through a two-step process requiring tryptophan hydroxylase and aromatic amino acid decarboxylase. Both enzymes are energy-dependent, and both require adequate cellular energy (ATP) and cofactors to function optimally.

PBM’s primary cellular effect — increasing ATP production through cytochrome c oxidase stimulation — could theoretically support serotonin synthesis by providing the energy substrate these enzymatic reactions require. Additionally, PBM has been shown to increase nitric oxide (NO) release, which can modulate serotonergic neurotransmission.

The Evidence

Xu et al. (2017) published a study in Neuroscience (321:138-149) examining transcranial PBM (810 nm) in a mouse model of depression. Mice receiving PBM showed significantly increased serotonin levels in the hippocampus and prefrontal cortex compared with untreated controls. The serotonin increase correlated with improvements in depression-like behaviours (forced swim test, tail suspension test).

Salehpour et al. (2018) reviewed transcranial PBM effects on brain neurochemistry in Molecular Neurobiology (55(8):6601-6636). The review noted that PBM at 810 nm wavelength increased serotonin levels in multiple brain regions in preclinical models, with the proposed mechanism involving enhanced tryptophan hydroxylase activity secondary to increased ATP availability.

Caldieraro and Cassano (2019) reviewed clinical evidence for transcranial PBM in mood disorders in Journal of Affective Disorders (243:262-273). They noted that the antidepressant effects observed in several small clinical trials are consistent with serotonergic modulation, though direct measurement of serotonin levels in human PBM studies has not been performed.

The honest summary: Animal studies demonstrate that transcranial PBM can increase brain serotonin levels. The mechanism (enhanced ATP production supporting serotonin synthesis) is biologically plausible. Human evidence is limited to observing antidepressant effects that are consistent with serotonergic modulation but could involve other pathways.

PBM and Dopamine

The Biological Rationale

Dopamine is synthesised from tyrosine through tyrosine hydroxylase (the rate-limiting enzyme) and aromatic amino acid decarboxylase. Like serotonin synthesis, this process is energy-dependent and could theoretically benefit from the enhanced cellular energy production that PBM provides.

The dopaminergic system is of particular interest because PBM has been studied more extensively for conditions involving dopamine dysfunction — notably Parkinson’s disease and depression — than for most other neurological applications.

The Evidence

Shaw et al. (2010) published a significant preclinical study in Experimental Neurology (226(1):120-127) examining transcranial near-infrared light (670 nm) in a mouse model of Parkinson’s disease (MPTP model). Treated mice showed significantly greater survival of dopaminergic neurons in the substantia nigra compared with untreated controls. This suggests PBM can protect dopamine-producing neurons from neurotoxic damage.

Moro et al. (2013) extended this work in Neuroscience Research (76(1-2):1-8), demonstrating that transcranial PBM at 670 nm preserved dopaminergic cells and maintained striatal dopamine levels in MPTP-treated mice. The neuroprotective effect was dose-dependent, with higher energy doses providing greater protection.

Hamilton et al. (2019) conducted a small pilot study of transcranial PBM in Parkinson’s disease patients, published in Neural Regeneration Research (14(6):1051-1053). Patients receiving 12 weeks of transcranial PBM showed improvements in motor symptoms, fine motor skills, and cognitive function. While the study was small and uncontrolled, the findings are consistent with dopaminergic support.

Cassano et al. (2016) studied transcranial PBM (810 nm) for major depressive disorder in a pilot RCT published in Psychological Medicine (46(7):1527-1535). Significant improvements in depression scores were observed, which the authors partially attributed to modulation of dopaminergic (as well as serotonergic) pathways.

The honest summary: PBM has demonstrated neuroprotective effects on dopaminergic neurons in animal models, preserving dopamine production in the face of neurotoxic challenge. Small human studies in Parkinson’s disease and depression show findings consistent with dopaminergic support. The evidence is more developed than for serotonin but still far from definitive.

PBM and Melatonin

The Circadian Connection

Melatonin’s relationship with light is well-established but nuanced in the context of PBM:

Conventional light-melatonin interaction: Blue-green light (460–490 nm) suppresses melatonin production via the retinal-SCN-pineal pathway. This is why screen use before bed disrupts sleep.

Red and near-infrared light do not suppress melatonin through the retinal pathway. The melanopsin photopigment in ipRGCs has minimal sensitivity to wavelengths above 600 nm. This means red light therapy can be used in the evening without disrupting the normal rise in melatonin that prepares the body for sleep.

Can PBM Actually Increase Melatonin?

Zhao et al. (2012) published a study in Sleep Medicine (13(10):1282-1287) examining the effects of red light (630 nm) exposure on sleep quality and melatonin levels in Chinese female basketball players. The red light treatment group showed significantly increased serum melatonin levels and improved sleep quality scores (Pittsburgh Sleep Quality Index) compared with controls. The proposed mechanism was stimulation of the pineal gland or enhancement of pineal metabolic function through increased cellular energy.

Naeser et al. (2014) studied transcranial LED therapy (633 nm + 870 nm) and noted improvements in sleep as a secondary outcome in patients with traumatic brain injury, published in Photomedicine and Laser Surgery (32(12):680-686). Sleep improvements are consistent with melatonin modulation, though melatonin was not directly measured.

The honest summary: One study directly demonstrated increased melatonin with red light exposure. The finding is biologically plausible — PBM could enhance pineal gland function through metabolic support without triggering the melanopsin-mediated suppression pathway that blue light activates. More replication is needed before this can be stated with confidence.

The Circadian Rhythm Context

Understanding how PBM interacts with the circadian system is practically important:

Morning and Daytime Use

PBM in the morning or during the day complements the natural circadian light cycle. The energy-enhancing effects (increased ATP, potential serotonin and dopamine support) align with the body’s daytime activity needs. Morning transcranial PBM may be particularly beneficial for mood and cognitive function.

Evening Use

Because red and near-infrared wavelengths do not suppress melatonin through the retinal pathway, evening PBM sessions are unlikely to disrupt sleep. In fact, the Zhao et al. (2012) study suggests evening red light exposure may actually support melatonin production. This gives PBM a significant practical advantage over blue-enriched light therapy boxes, which must be used in the morning to avoid sleep disruption.

Implications for Shift Workers and Jet Lag

For individuals with disrupted circadian rhythms (shift workers, frequent travellers), the ability of red light therapy to potentially support neurotransmitter balance without disrupting melatonin timing is theoretically attractive. However, no clinical trials have specifically tested PBM for circadian disruption in these populations.

Protocol for Neurotransmitter Support

Transcranial PBM Protocol

Wavelength: 810 nm (near-infrared) is the most studied wavelength for transcranial PBM. This wavelength penetrates the skull more effectively than shorter red wavelengths.

Application sites:

• Forehead (prefrontal cortex) — relevant to mood, executive function, and serotonergic/dopaminergic pathways
• Temporal regions — access to temporal cortex and underlying structures
• Vertex (top of head) — access to motor cortex and central brain structures

Energy density: 10–30 J/cm² per treatment site (transcranial applications typically use higher doses than superficial tissue treatment because the skull attenuates a significant proportion of the light)

Treatment time: 10–20 minutes per session

Frequency: 3–5 sessions per week

Device considerations: For transcranial PBM, use a device with verified NIR output (810–850 nm). Small panels, targeted devices, or helmet-style devices designed for transcranial use are most practical. Ensure the device is positioned close to the scalp (< 5 cm) for maximum transcranial penetration.

General Mood and Energy Support

For broader neurotransmitter support (serotonin, dopamine, energy metabolism), whole-body or large-area PBM can provide systemic benefits:

Wavelengths: 660 nm (red) + 850 nm (NIR) combination Treatment time: 15–20 minutes Frequency: Daily or 5 times per week Timing: Morning sessions may be optimal for mood and alertness benefits

Evening Sleep Support

Wavelength: 630–660 nm (red only — avoid strong NIR directly before bed as its energising effects may delay sleep onset in some individuals) Treatment time: 10–15 minutes Timing: 1–2 hours before bed Note: This is the least evidence-supported protocol on this page; the Zhao (2012) study is encouraging but has not been replicated

Important Limitations and Caveats

PBM Is Not a Replacement for Mental Health Treatment

If you have clinical depression, anxiety disorder, bipolar disorder, or any other diagnosed mental health condition, PBM should not replace evidence-based treatment (medication, psychotherapy, or both). The clinical evidence for PBM in mood disorders is early-stage and insufficient to recommend it as a primary treatment.

Most Evidence Is Preclinical

The neurotransmitter evidence is strongest in animal models. Human studies have demonstrated clinical effects (improved mood, better sleep) that are consistent with neurotransmitter modulation, but direct measurement of serotonin and dopamine levels in living human brains is not practically possible with current technology.

Individual Variation Is Likely Significant

Neurotransmitter systems are highly individual. Genetic variations in serotonin and dopamine receptor density, enzyme activity, and transporter function mean that the same PBM protocol could produce different neurochemical effects in different people.

The Dose-Response Relationship Is Not Well Defined

For transcranial PBM, the optimal dose for neurotransmitter effects has not been established. There is a biphasic (hormetic) dose-response in PBM generally — too little light has no effect, too much can be counterproductive. The protocols above are based on the parameters used in published studies but should not be considered definitively optimised.

The Honest Assessment

The connection between PBM and neurotransmitter production is real but early in its scientific development. The biological mechanisms are sound: increasing cellular energy production through cytochrome c oxidase stimulation plausibly supports the energy-dependent enzymatic processes that synthesise serotonin, dopamine, and melatonin. Animal studies confirm these effects. Small human trials show clinical outcomes consistent with neurotransmitter modulation.

What we lack is large-scale human evidence directly measuring neurotransmitter changes in response to PBM. Until that evidence exists, claims about red light therapy “boosting serotonin” or “increasing dopamine” should be treated as mechanistically plausible hypotheses rather than established facts.

That said, PBM has an excellent safety profile, no meaningful side effects at recommended doses, and no drug interactions. For individuals interested in supporting mood, cognitive function, and sleep quality through non-pharmacological means, incorporating PBM into a broader wellness strategy (alongside exercise, sleep hygiene, nutrition, and social connection) is a reasonable and low-risk approach.

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This article is for informational purposes only and does not constitute medical advice. If you are experiencing symptoms of depression, anxiety, or other mental health conditions, consult a qualified healthcare professional. Do not alter prescribed medication without medical guidance.