Sleep supplements: melatonin in the UK, how much melatonin to take, and what else works

First: when supplements won’t help

Sleeping badly three or more nights a week for three months is chronic insomnia. Guidelines name cognitive behavioural therapy for insomnia (CBT-I) as the first-line treatment, not pills or supplements. Ask your GP about it. Loud snoring with pauses in breathing, restless legs, depression and anxiety also need a doctor rather than a supplement.

Supplements make more sense when the problem is short-lived: crossing time zones, a broken routine, stress before a big event.

Melatonin in the UK: prescription only

Melatonin is a hormone your body makes in the evening as it gets dark. It doesn’t switch the brain off like a sleeping pill. It signals that it’s time to sleep, which is why it works best when your body clock is out of step.

In the UK, melatonin is a prescription-only medicine. The MHRA (the medicines regulator) says it poses “an identifiable risk to public/patient safety” and treats any product that contains it as a medicine. Selling it without a prescription is illegal. A Which? investigation in early 2026 still found it listed on large online marketplaces, some with claimed doses of 10–30 mg.

What the NHS prescribes:

• Short-term insomnia, mainly in people aged 55 and over: one 2 mg slow-release tablet 1–2 hours before bed. Courses usually last 1–4 weeks, and 13 weeks at most.
• Jet lag: one 3 mg tablet at your usual bedtime after you arrive (not before 8pm or after 4am), for up to 5 days. The dose can go up to 6 mg.
• Long-term sleep problems in children and some adults: only through a specialist.

In the EU, the rules differ between countries. Some sell low-dose melatonin as a food supplement, others treat it as a medicine. iHerb says it tries to block products that aren’t allowed in your country, but checking the rules is still your job.

How much melatonin should you take?

Less than most bottles suggest. EFSA has confirmed two effects. First, 1 mg taken shortly before bed shortens the time it takes to fall asleep. Second, at least 0.5 mg close to bedtime on the first day of travel and for a few days after arrival eases jet lag. On average the gain is minutes, not hours.

Supplements abroad range from 0.3 mg to 10 mg and more. There’s no good evidence that higher doses work better, and they more often leave you groggy in the morning. Where melatonin is legal as a supplement, start with 0.5–1 mg 30–60 minutes before bed.

Quality varies. In a 2017 Canadian study, the actual melatonin content of supplements ranged from 83% less to 478% more than the label claimed.

Talk to a doctor first if you’re pregnant or breastfeeding, choosing for a child, have epilepsy or an autoimmune condition, or take blood thinners, sleeping pills, sedatives or anti-seizure drugs.

L-theanine for sleep and stress

L-theanine is an amino acid from tea leaves. Studies usually gave 200 mg. Some participants reported less stress and better sleep quality. The effect is small, and most studies were short and small. Theanine doesn’t make you drowsy, so it suits people kept awake by racing thoughts.

Glycine and magnesium

In small Japanese studies, 3 g of glycine before bed improved how people rated their sleep and how they felt the next morning. The data is limited, but glycine is cheap and well tolerated. As a powder, 3 g is easy to measure. Doses and studies are in our guide to glycine for sleep.

Magnesium is often suggested for sleep, but the evidence is thin. Any benefit is most likely in people who are low in it. If your diet is short on nuts, beans and wholegrains, magnesium glycinate in the evening is a reasonable option. Forms and doses are covered in our guide to types of magnesium.

Valerian, chamomile and other herbs

Valerian studies are inconsistent. Some show a small benefit, others no difference from placebo. They’re hard to compare because extracts and doses vary widely. Chamomile, lemon balm and passionflower are even less studied. For occasional use they’re generally safe, but they won’t act like a sleeping pill.

Ashwagandha and 5-HTP: use with care

In several trials, ashwagandha slightly improved sleep and reduced stress. But rare cases of liver injury have been reported. It can affect thyroid hormones, and it shouldn’t be used in pregnancy. Denmark banned it in supplements in 2023, and it is also barred from supplements in the Eurasian Economic Union. Read our ashwagandha side effects guide and talk to a doctor first, especially with thyroid, liver or autoimmune conditions.

5-HTP is sometimes sold for sleep and mood. It acts on serotonin, so don’t combine it with antidepressants without your doctor. More in our guide to 5-HTP side effects.

Sleep supplements compared

Ground rules for any sleep supplement:

• Start with the lowest dose.
• Change only one supplement at a time.
• Use it for weeks, not months.
• Check interactions with your medicines, especially sleeping pills and sedatives.

How to choose a sleep supplement on iHerb

1. Match it to the problem. Evening tension calls for L-theanine; light sleep for glycine; a low-magnesium diet for magnesium glycinate. For jet lag or ongoing insomnia in the UK, see your GP about melatonin.
2. Choose single-ingredient products. “Sleep complexes” often hold 5–10 ingredients in small doses, so you can’t tell what works or what causes a side effect.
3. Check the label for hidden melatonin if you live in the UK.
4. Check interactions with any medicine you take.

This made-up “sleep blend” label shows what to look for, line by line:

How to read the label, and why “Serving size” matters, is explained in our label guide. More options for stress and sleep are in the sleep and stress section.