Melatonin

How it works

It activates MT1 and MT2 melatonin receptors in the suprachiasmatic nucleus, reinforcing the endogenous circadian signal that promotes sleep onset and entrains the sleep-wake cycle.

Prescribing in practice

• Brands and formulations are not interchangeable (immediate- versus modified-release behave differently), so prescribe by brand and avoid switching without intent.
• It may cause daytime drowsiness; warn about driving and operating machinery, particularly when first started.
• Caution and dose review are needed in hepatic impairment and with potent CYP1A2 inhibitors such as fluvoxamine, which markedly raise melatonin levels.

Monitoring

No routine laboratory monitoring is required; review clinical response to sleep and continued need periodically rather than continuing indefinitely.

Counselling the patient

• Take shortly before bedtime and avoid alcohol, which reduces its effectiveness.
• Swallow modified-release tablets whole unless a specific formulation is licensed to be dispersed.
• Use alongside good sleep hygiene rather than as a sole measure.

Evidence & guidelines

NICE supports time-limited melatonin in defined groups such as older adults with insomnia and children with neurodevelopmental sleep problems, with regular review of ongoing need.