Sleep hormone
Melatonin
Also searched as Melatonin.
You want it timed and present: well-timed melatonin is the conductor of healthy sleep and circadian rhythm.
In depth
Melatonin — the hormone of biological night that entrains the body clock and opens the gate to sleep.
What drives it
Mood (serotonin) increases it.
Serotonin modulates melatonin synthesis, PNAS 2021 — serotonin induces AANAT, the rate-limiting step in its conversion to melatonin. doi 10.1073/pnas.2113852118
Alertness chemical increases it.
NBK550972 — ,Noradrenaline is the alerting transmitter here, driving the Noradrenergic Tone → Sustained Attention link and the Noradrenergic Tone → ADHD link. It is also what makes melatonin. Norepinephrine, through activation of beta receptors, stimulates the synthesis of melatonin from serotonin in the pineal gland, which is characterized by a rich noradrenergic innervation. The suprachiasmatic clock controls the release of norepinephrine from the dense pineal sympathetic afferents at night. Mechanism to the enzyme: cAMP/PKA signaling phosphorylates AANAT, the rate-limiting enzyme of melatonin synthesis. And the off-switch is the same lever: during daylight, when norepinephrine stimulation ceases, degradation of that enzyme occurs rapidly. So a single transmitter runs both daytime alertness and night-time melatonin synthesis, in different tissues, on different schedules.
Motivation reduces it.
10.1371/journal.pbio.1001347 — ,Enumeration 1 gave this pathway its catecholamine arm. Enumeration 3 gave it the circadian arm. This edge is where they meet. The mechanism is a direct receptor-receptor interaction: through alpha-1B-D4 and beta-1-D4 receptor heteromers, dopamine inhibits adrenergic receptor signaling and blocks the synthesis of melatonin induced by adrenergic ligands. The adrenergic receptors are the bridge between circadian norepinephrine release and pineal melatonin output, and dopamine reaches in and closes that bridge. And the receptor is D4 — the classic ADHD candidate gene. DRD4 is the dominant dopamine receptor gene expressed in the pineal gland, at levels greater than in other tissues, with circadian expression under photoneural control. A gene long studied for its ADHD association turns out to sit at the junction of the dopamine and melatonin systems, which is exactly where this pathway needed a bridge. At some hours the interaction does not exist at all. The authors call it the first example of a circadian-controlled receptor heteromer. Direction depends on receptor family, also in the conditional table: D1-like receptors stimulate adenylate cyclase and promote aanat, the key melatonin-synthesis enzyme, while D2-like (D2, D3, D4) inhibit it. And the axis is reciprocal: melatonin signaling decreases dopamine release while dopamine inhibits pineal melatonin output — antagonistic feedback that stabilizes circadian oscillation. doi 10.1371/journal.pbio.1001347
What it drives
It increases Body clock.
Melatonin/SCN study 2001, Am J Physiol Cell Physiol 280:C110 — melatonin phase-advances the suprachiasmatic circadian clock via MT2 receptor signaling. doi 10.1152/ajpcell.2001.280.1.C110
It increases Sleep.
Melatonin, produced by the pineal gland at night, serves as a time CUE to the biological clock and promotes sleep anticipation via the brain default mode network, explaining increased sleep propensity in circadian rhythm sleep disorders. Scope, stated in the same literature: melatonin prevents arousal and promotes sleep -- but does not induce it (PMC6057894). It is a chronobiotic time signal, not a hypnotic, and should never be presented as one. PMC6057894
It reduces Attention regulation.
DIM-light melatonin onset is delayed by approximately 45 minutes in children and 90 minutes in adults with ADHD, with up to 75 percent of adults with childhood-onset ADHD showing delayed DLMO. This is a clock reading, not a questionnaire. It travels with other rhythm markers: blunted and delayed cortisol rhythms, reduced pineal volume, and attenuated peripheral clock-gene rhythms (BMAL1, PER2), with genetic studies implicating per and clock polymorphisms. And it is the only arm on this pathway with a non-drug intervention signal: melatonin and bright light therapy have advanced DLMO in both children and adults with ADHD, and emerging data correlate phase advancement with ADHD symptom improvement. Scope, stated by the authors: that correlation is emerging, and the proposed clinical pathway is behavioral-first — fixed wake times, morning bright light, evening light restriction — with melatonin selective and low-dose for confirmed or probable DLMO delay. It is a phase-shifting tool, not a sedative, and not a treatment for the disorder. PMC12728042
It reduces Sustained focus.
daytime melatonin and light independently affect human alertness and body temperature. doi 10.1111/jpi.12583
It reduces Lowers cortisol.
melatonin also suppresses GR nuclear translocation by maintaining the GR in a complex with heat shock protein 90; melatonin, directly and/or epigenetically, can upregulate BAG-1. PMC10645470
It reduces Motivation.
Dopamine has an inhibitory effect on melatonin release, while melatonin also inhibits dopamine release - that is a mutual inhibition. Both arrows are drawn, and the pair forms a switch. Mutual inhibition is a switch, not a dimmer: two stable states with a threshold between them, which is the correct shape for a nocturnal/diurnal transition. doi 10.37349/ent.2023.00062
It reduces Night-time blood pressure.
Nocturnal melatonin release lowers sympathetic outflow and supports the night-time fall in blood pressure. doi 10.2147/vhrm.s24603
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.