Sleep
What the NHS, NICE and the Royal College of Psychiatrists say about melatonin, valerian, magnesium and other supplements sold for sleep.
The NHS says insomnia usually gets better by changing sleeping habits, and a GP may offer cognitive behavioural therapy. Pharmacy sleep aids, some containing valerian, are for 1 to 2 weeks at most. Melatonin is a prescription-only medicine in the UK, and melatonin supplements are not authorised for sale here. For the other supplements sold for sleep, from magnesium to ashwagandha, the sources below find the evidence limited, and they flag safety concerns about L-tryptophan.
NICE: Names cognitive behavioural therapy as the first-line option for long-term insomnia.
Each line below is a short summary of what the named source says, with a link to read it in full. None of it is medical advice.
Limited evidence
Magnesium
A mineral found in spinach, nuts and wholemeal bread, among other foods.
- NCCIH: Very little research on insomnia; studies so far are low quality with conflicting findings.
- Harvard Health: Clinical studies have not shown a consistent effect on sleep.
L-theanine
An amino acid found mostly in tea leaves, and in some mushrooms.
- Cleveland Clinic: Research is not conclusive: small, short studies with inconsistent findings.
- Cleveland Clinic: Not shown to bring on sleep directly; some studies combined it with other ingredients.
Also covered by Mind.
Tart cherry
The sour cherry used in pies and baking, sold as juice, concentrate, capsules and gummies.
- Cleveland Clinic: Little rigorous research: a few very small studies, and more research is needed.
- Cleveland Clinic: Doses in capsules and gummies can vary; the fruit or juice is recommended instead.
CBD
Cannabidiol, one of the chemicals called cannabinoids, found in hemp and cannabis plants.
- NCCIH: Insufficient evidence for any sleep disorder; research is scarce and mostly at risk of bias.
- Food Standards Agency: Think carefully before taking it; healthy adults should keep to 10mg a day at most.
Also covered by Mind.
Advised against
Melatonin
A hormone the body makes, with levels rising at night. In the UK, melatonin is a prescription-only medicine.
Things to check
- NHS: Some pharmacy sleep aids can make you drowsy, which could make driving difficult; check with your doctor before taking anything for sleep.
- NHS: If you are prescribed melatonin, do not take other medicines or herbal remedies that make you sleepy.
- RCPsych: Valerian can cause drowsiness, making it dangerous to drive, and can interact with other drugs; speak to a doctor before taking it.
- NCCIH: L-tryptophan may cause life-threatening serotonin toxicity when taken with medicines that affect serotonin.
- NHS: Having 400mg or less a day of magnesium from supplements is unlikely to cause any harm.
- NIH ODS: Ashwagandha has been linked to liver injury in some people, and may not be safe in pregnancy or while breastfeeding.
- Food Standards Agency: CBD is not recommended for children, or anyone taking medication, trying to conceive, pregnant or breastfeeding, unless under medical direction.
- NHS: Check a herbal medicine has a THR mark, and check with a pharmacist first if you already take other medicines.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
Sources
- InsomniaSymptoms and causes of insomnia, changing sleeping habits, pharmacy sleep aids and seeing a GP.
- Common questions about melatoninMelatonin as a prescription medicine, including whether melatonin supplements can be bought in the UK.
- Insomnia: Scenario: Managing insomniaNICE's summary for GPs on managing short- and long-term insomnia, including over-the-counter medicines.
- Sleeping wellSleep problems and their treatments, including melatonin, valerian and remedies sold without a prescription.
- Complementary and alternative medicines: herbal remediesHerbal remedies and supplements used for mental health, sleep and memory, with side effects and interactions.
- Herbal medicines and complementary therapiesWhat herbal medicines are, who should avoid them, and checking them with a pharmacist.
- Herbal remediesWhat herbal remedies are, how they are licensed in the UK, and when they may be unsuitable.
- Types of complementary and alternative therapiesComplementary therapies people use for mental health and sleep, including 5-HTP, L-theanine and CBD.
- Vitamins and minerals - OthersOther vitamins and minerals, including how much magnesium is safe to take.
- Sleep Disorders and Complementary Health Approaches: Usefulness and SafetyThe evidence and safety of complementary approaches for insomnia, from melatonin and magnesium to valerian and CBD.
- Valerian: Usefulness and SafetyWhat is known about valerian's usefulness and safety.
- Ashwagandha: Is it helpful for stress, anxiety, or sleep?The research on ashwagandha for stress, anxiety and sleep, and its safety.
- What Is L-Theanine? Potential Benefits, Risks and What the Science SaysWhat L-theanine is, where the research on it stands, and its risks.
- Tart Cherry Juice for Sleep: Does It Really Work?What the research says about tart cherry and sleep, and who may want to avoid it.
- Cannabidiol (CBD)The Food Standards Agency's advice on CBD sold as food and food supplements.
- Melatonin or magnesium: Can either supplement help you sleep?Melatonin and magnesium for sleep: the evidence, side effects and who should avoid each.
Sources checked 28 September 2026. Prices checked 20 October 2026, ranked purely by price per dose. Which sources these pages use.