Melatonin is a hormone your brain produces in response to darkness, signalling to your body that it is time to sleep. Supplemental melatonin is used mainly to help shift sleep timing, such as with jet lag or delayed sleep phase, rather than as a general sleep aid for everyone.
Evidence supports melatonin for circadian timing issues (jet lag, shift work, delayed sleep phase) at relatively low doses. Evidence for melatonin improving sleep quality in people without a timing problem is weaker and less consistent. In the UK, melatonin is prescription-only for adults, unlike in some other countries.
Generally well tolerated short-term at low doses. Can cause grogginess, headache or vivid dreams. Higher-than-needed doses do not necessarily work better and may worsen side effects. Long-term use in children and adolescents needs specific medical guidance.
Before use, since melatonin is prescription-only in the UK for adults. Speak to a doctor about persistent sleep problems rather than sourcing melatonin informally.
Varies by prescription and formulation.
NHS and MHRA guidance on melatonin prescribing status in the UK. Circadian rhythm research on melatonin timing and dosing. Educational information only. Melatonin is prescription-only for adults in the UK.