Melatonin is a hormone your brain produces when it gets dark outside. Your pineal gland releases it to help regulate your circadian rhythm, that 24-hour internal clock controlling when you feel awake and when you feel sleepy. Exposure to light at night suppresses melatonin production, which partly explains why staring at your phone before bed can make it harder to fall asleep.

Beyond sleep, melatonin appears to do quite a lot in the body. It’s found in the retina, bone marrow, gut, skin and immune cells, not just the brain. Receptors for melatonin are scattered throughout the body, suggesting it influences reproduction, immune function, energy balance and even mood. It also acts as an antioxidant, neutralising harmful reactive oxygen species.

What form does supplemental melatonin come in?

Most melatonin supplements sold today are synthetic, though some are derived from animal pineal glands or microorganisms. The synthetic version is generally preferred because it avoids the contamination risks associated with animal-derived products.

In the UK, melatonin is classified as a prescription-only medicine, while in many other countries it’s sold over the counter as a dietary supplement. This difference matters because it affects quality control and medical oversight.

What dose should you take?

If you’re considering melatonin, starting low makes sense. A dose of 0.5mg to 1mg taken 30 minutes before bed is a reasonable starting point. If that doesn’t help after a few nights, you can try increasing to 3mg or 5mg.

Here’s something counterintuitive: taking more melatonin doesn’t necessarily help you fall asleep faster. Research suggests that physiological doses (0.3mg to 1mg) often work as well as, or better than, higher pharmacological doses. The goal is finding the lowest dose that works for you, not taking as much as possible.

What are the potential benefits of melatonin?

1. Primary sleep disorders

Primary insomnia means difficulty sleeping that isn’t caused by another medical condition, mental health issue or medication. According to the diagnostic criteria, you need trouble falling asleep or staying asleep for at least a month, with daytime impairment as a result.

A Cochrane review of 13 trials found that melatonin reduced time to fall asleep by about 7 minutes on average and increased total sleep time modestly [1]. I should be honest here: 7 minutes isn’t dramatic. But for people who lie awake for hours, even small improvements can compound over time. The NHS notes melatonin can help reset your body clock and is sometimes prescribed for insomnia, particularly in adults over 55 [2].

2. Secondary sleep disorders

When sleep problems stem from an underlying condition, they’re called secondary. This includes insomnia linked to pain conditions, thyroid disorders, acid reflux, lung disease, kidney problems or neurological issues like Parkinson’s disease.

A meta-analysis published in PLOS ONE found that melatonin improved sleep quality in people with various secondary sleep disorders, though the effect sizes varied considerably [3]. The evidence is stronger for some conditions than others. People with fibromyalgia or chronic pain conditions may benefit more than those whose insomnia stems from medication side effects.

If you have nocturia (waking frequently to urinate at night), melatonin might help with the sleep disruption, though it won’t address the underlying bladder issue.

3. Blood pressure regulation

Blood pressure naturally dips at night when melatonin is high. Some researchers wondered whether melatonin supplements might help people whose blood pressure doesn’t follow this normal nocturnal pattern.

A meta-analysis of controlled trials found that melatonin supplementation reduced both systolic and diastolic blood pressure, particularly in people with diabetes [4]. The effect was modest but consistent. This doesn’t mean melatonin should replace blood pressure medication, but it’s an interesting finding worth discussing with your doctor if you take antihypertensives.

4. Fibromyalgia

Fibromyalgia causes widespread pain, fatigue and sleep disturbances. About 75% of people with fibromyalgia report significant sleep problems, which can worsen pain perception.

Several small trials have tested melatonin in fibromyalgia patients. The results suggest it may reduce pain severity and improve sleep quality [5]. One study found 5mg of melatonin at bedtime was more effective than 3mg for pain relief. The mechanism isn’t entirely clear, but melatonin’s effects on both sleep architecture and pain pathways may both contribute.

5. Blood lipid levels

Dyslipidaemia, the medical term for abnormal blood fats, increases cardiovascular disease risk. Some research suggests melatonin might improve cholesterol profiles.

A systematic review found melatonin supplementation was associated with reductions in triglycerides and total cholesterol, particularly in people with metabolic disorders [6]. The effects were small but statistically significant. I wouldn’t rely on melatonin to manage dyslipidaemia, but it’s worth noting as a potential secondary benefit for people taking it for sleep.

6. Blood sugar control

Type 2 diabetes affects glucose regulation, and poor sleep makes glycaemic control worse. Melatonin receptors exist on pancreatic beta cells, suggesting a direct role in insulin secretion.

Research findings here are mixed. Some studies show improved fasting glucose and HbA1c with melatonin supplementation [7], while others show no significant effect. The benefits seem more pronounced in people with metabolic syndrome or those with disrupted circadian rhythms. If you have diabetic bladder dysfunction or other diabetes complications, this might be relevant to discuss with your endocrinologist.

7. Cancer treatment support

This one needs careful framing. Melatonin is not a cancer treatment. However, research has examined whether it might help as an adjunct to conventional therapy.

A meta-analysis of randomised controlled trials found that melatonin supplementation alongside chemotherapy or radiotherapy was associated with improved tumour response rates and reduced treatment side effects [8]. Patients reported less fatigue, fewer mouth sores and better sleep. The authors cautioned that publication bias might inflate these findings, and melatonin should never replace standard oncology care.

8. Jet lag

This is where melatonin has its strongest evidence base. When you cross multiple time zones, your internal clock gets out of sync with local time. Melatonin can help reset it.

A Cochrane review concluded that melatonin is “remarkably effective” for preventing or reducing jet lag when taken close to the target bedtime at your destination [9]. It works best for eastward travel (when you’re trying to advance your sleep schedule) and for trips crossing five or more time zones. Taking 0.5mg to 5mg at bedtime for the first few days after arrival helps most people adjust faster.

9. Mood disorders

Depression often involves disrupted circadian rhythms and sleep problems. Researchers have investigated whether melatonin or its analogues might help.

The results are disappointing for melatonin itself. Studies haven’t shown it improves depressive symptoms independently of sleep effects [10]. However, agomelatine, a prescription antidepressant that acts on melatonin receptors, does show antidepressant effects, suggesting the melatonin system plays some role in mood regulation.

10. Primary headache prevention

Migraine and cluster headaches have circadian patterns, with attacks often occurring at predictable times. This led researchers to test whether melatonin might help prevent them.

The evidence is limited and inconsistent. Some small trials showed reduced migraine frequency with melatonin, while others showed no benefit [11]. For cluster headaches, which often strike at night, there’s a bit more rationale, but large quality trials are lacking. The NHS doesn’t recommend melatonin for headache prevention based on current evidence [2].

11. Pain management

Melatonin has analgesic properties that appear independent of its sleep effects. It interacts with opioid receptors and modulates pain signalling pathways.

Studies in surgical patients found that preoperative melatonin reduced postoperative pain intensity and opioid requirements [12]. For chronic pain conditions, the evidence is more mixed. There’s enough here to warrant further research, but not enough to recommend melatonin specifically for pain relief.

12. Alzheimer’s disease

People with Alzheimer’s often experience severe sleep disruption, including wandering at night and excessive daytime drowsiness. Their melatonin levels are often abnormally low.

Studies suggest melatonin can improve sleep quality in Alzheimer’s patients without significant adverse effects [13]. It may also have neuroprotective properties, though whether it affects disease progression remains unclear. For carers dealing with nighttime behavioural problems, melatonin is worth discussing with the patient’s neurologist.

Side effects of melatonin

For most adults, short-term melatonin use appears safe. The most common side effects are:

Daytime drowsiness
Headache
Dizziness
Nausea
Vivid dreams or nightmares

These tend to be dose-dependent, occurring more often at higher doses. Long-term safety data is limited because most trials lasted only a few weeks.

Some people report more vivid or lucid dreams while taking melatonin. This isn’t necessarily problematic unless the dreams are disturbing.

Safety precautions and drug interactions

Here’s where things get important. Melatonin interacts with quite a few medications and isn’t appropriate for everyone.

Who should avoid melatonin:

Pregnant and breastfeeding women should not take melatonin. There isn’t enough safety data, and melatonin crosses the placenta.
Children shouldn’t use melatonin without medical supervision. While it’s sometimes prescribed for specific sleep disorders in children, over-the-counter use isn’t recommended.
People with liver or kidney disease may not metabolise melatonin properly, leading to accumulation.
Those with autoimmune conditions should be cautious, as melatonin can stimulate immune function.

Drug interactions to watch for:

Blood pressure medications: Melatonin can lower blood pressure. If you take antihypertensives, particularly nifedipine, the combination may cause excessive blood pressure drops.
Blood thinners and antiplatelet drugs: Melatonin may slow blood clotting. Avoid combining it with warfarin, aspirin, clopidogrel, ibuprofen, naproxen, heparin or enoxaparin without medical advice.
Diabetes medications: Melatonin can affect blood glucose levels. If you take insulin, metformin, glimepiride, glyburide or other diabetes drugs, monitor your blood sugar more carefully.
Immunosuppressants: Because melatonin may enhance immune function, it could theoretically reduce the effectiveness of drugs like cyclosporine, tacrolimus, azathioprine or corticosteroids.
Sedatives and sleeping pills: Combining melatonin with other CNS depressants increases drowsiness risk. This includes benzodiazepines like diazepam and lorazepam, as well as zolpidem and other sleep medications.
Fluvoxamine: This antidepressant significantly increases melatonin levels by inhibiting its metabolism. Taking supplements on top could cause excessive effects.
Contraceptive pills: Oral contraceptives increase natural melatonin production, so adding supplements may lead to higher than expected levels.
Caffeine: Here’s an interesting one. Caffeine reduces melatonin levels, potentially undermining supplementation. If you drink coffee in the afternoon, it may still be affecting your melatonin at bedtime.
Verapamil: This calcium channel blocker may reduce melatonin’s effectiveness by competing for metabolism.
Flumazenil: This benzodiazepine reversal agent may block melatonin’s effects.

Practical precautions:

Don’t drive or operate machinery after taking melatonin. It causes drowsiness, which is rather the point.
Consult your doctor before starting melatonin if you have any chronic condition. This is especially important for interstitial cystitis, overactive bladder or other conditions where sleep disruption is secondary to physical symptoms.
Don’t assume more is better. Higher doses don’t improve effectiveness and may cause more side effects.
Time it correctly. Taking melatonin too early or too late reduces its effectiveness for sleep.

The bottom line

Melatonin works best for jet lag and circadian rhythm problems. For general insomnia, the effects are real but modest. It’s not a sleeping pill in the traditional sense; it signals to your body that it’s time for sleep rather than forcing unconsciousness.

If you’re interested in other sleep-supporting supplements, you might also look at valerian, L-theanine, GABA or tryptophan. Each works through different mechanisms and may be worth trying if melatonin doesn’t suit you.

For broader strategies on managing sleep problems, see our article on alternative therapies for insomnia.

References

Ferracioli-Oda E, Qawasmi A, Bloch MH. Meta-analysis: melatonin for the treatment of primary sleep disorders. PLoS One. 2013;8(5):e63773.
NHS. Melatonin for sleep problems. NHS website. Available at: https://www.nhs.uk/medicines/melatonin/
Li T, Jiang S, Han M, et al. Exogenous melatonin as a treatment for secondary sleep disorders: A systematic review and meta-analysis. Front Neuroendocrinol. 2019;52:22-28.
Grossman E, Laudon M, Zisapel N. Effect of melatonin on nocturnal blood pressure: meta-analysis of randomized controlled trials. Vasc Health Risk Manag. 2011;7:577-584.
de Zanette SA, Vercelino R, Laste G, et al. Melatonin analgesia is associated with improvement of the descending endogenous pain-modulating system in fibromyalgia: a phase II, randomized, double-dummy, controlled trial. BMC Pharmacol Toxicol. 2014;15:40.
Mohammadi-Sartang M, Ghorbani M, Mazloom Z. Effects of melatonin supplementation on blood lipid concentrations: A systematic review and meta-analysis of randomized controlled trials. Clin Nutr. 2018;37(6 Pt A):1943-1954.
Delpino FM, Figueiredo LM, Nunes BP. Effects of melatonin supplementation on diabetes: A systematic review and meta-analysis of randomized clinical trials. Clin Nutr. 2021;40(7):4595-4605.
Wang YM, Jin BZ, Ai F, et al. The efficacy and safety of melatonin in concurrent chemotherapy or radiotherapy for solid tumors: a meta-analysis of randomized controlled trials. Cancer Chemother Pharmacol. 2012;69(5):1213-1220.
Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520.
Hansen MV, Danielsen AK, Hageman I, et al. The therapeutic or prophylactic effect of exogenous melatonin against depression and depressive symptoms: a systematic review and meta-analysis. Eur Neuropsychopharmacol. 2014;24(11):1719-1728.
Long R, Zhu Y, Zhou S. Therapeutic role of melatonin in migraine prophylaxis: A systematic review. Medicine (Baltimore). 2019;98(3):e14099.
Andersen LP, Werner MU, Rosenberg J, et al. A systematic review of peri-operative melatonin. Anaesthesia. 2014;69(10):1163-1171.
McCleery J, Cohen DA, Sharpley AL. Pharmacotherapies for sleep disturbances in dementia. Cochrane Database Syst Rev. 2016;11(11):CD009178.