Melatonin

Mechanism of action

Agonism of MT1 and MT2 receptors (GPCRs) in the suprachiasmatic nucleus and other areas: MT1 promotes sleep onset by reducing the wakefulness signal, while MT2 contributes to circadian synchronization/phase shifting. It also modulates thermoregulation (reduction of core body temperature), the hypothalamic-pituitary-gonadal axis indirectly, and shows antioxidant/anti-inflammatory activity in experimental models (radical scavenging and regulation of antioxidant enzymes), with clinical relevance still undefined for many extra-sleep indications.

Supported benefits

• Reduction of jet lag symptoms and improved adaptation to the new time zone (especially eastward travel) (strong)
• Improved sleep onset latency and/or sleep quality in some forms of insomnia, with generally small but significant average effects in meta-analyses (moderate)
• Circadian rhythm disorders (e.g. delayed phase, shift work sleep-wake disorder): support for realignment when used with appropriate timing and light hygiene (moderate)
• Improved sleep in some specific populations (e.g. older adults; certain neuropsychiatric or neurodevelopmental conditions), with study heterogeneity (limited)
• Effects on cardiometabolic, immune, or pain/inflammation parameters: preliminary and inconclusive results (emerging)

Safety & side effects

• Daytime drowsiness, reduced alertness, slowed reaction times (risk for driving/operating machinery)
• Headache, dizziness
• Nausea or gastrointestinal disturbances
• Vivid dreams/nightmares
• Irritability or mood changes in susceptible individuals (rare but reported)
• Possible transient worsening of sleep quality if timing/dose are not appropriate (e.g. taking it too late)

FAQ

Does melatonin “make you sleep” like a sleeping pill?

It acts primarily as a circadian signal (chronobiotic) and may facilitate falling asleep in some conditions, but it is not a classic sedative. The effect depends greatly on timing relative to the biological rhythm and light exposure.

Why does it sometimes not work or make sleep worse?

Common causes include timing not aligned with one’s circadian rhythm, exposure to bright light in the evening, a dose/formulation not suited to the goal (sleep onset vs sleep maintenance), or individual variability in metabolism.

Is it useful for jet lag?

The evidence is solid for reducing jet lag symptoms and facilitating adaptation, especially if taken close to the sleep time of the new time zone and combined with light management strategies.

Is there a risk of dependence or tolerance?

It is not typically associated with dependence like some hypnotics. However, repeated use can lead to “behavioral dependence” (psychological habit), and effectiveness may vary over time if circadian/environmental factors are not corrected.

What is the difference between immediate-release and extended-release?

Immediate-release rapidly increases levels and tends to be more geared toward sleep onset latency; extended-release aims to maintain more stable levels during the night, more similar to the physiological profile.