The guide

Is melatonin safe? Side effects, medicines, children and the heart study

By GyroscopeUpdated November 14, 202619 sources

In trials lasting a few weeks, melatonin’s side effects were mild and uncommon, mostly daytime sleepiness, headache and dizziness. The real cautions are a few medicines it interacts with, pregnancy and breastfeeding, where it hasn’t been studied, and small children, who swallow it more every year. The heart failure headline came from a conference abstract that hadn’t been peer reviewed, and it can’t show melatonin caused anything.

For a healthy adult taking a small dose for a few weeks, the risks in the trials are small. The open question is years of nightly use, which nobody has studied well.

The safest melatonin is the kind your own brain makes, and nobody needs a doctor’s note for daylight and a dark bedroom. How to increase melatonin naturally has the habits, at their real size.

What side effects do people get?

The biggest review pooled 37 randomized trials, at doses from 0.15 to 12 mg a day. People were followed for up to 29 weeks, but most trials lasted 4 weeks or less.

A few rarer effects were judged more significant: agitation, tiredness, mood swings, nightmares, skin irritation and palpitations. Most effects went away on their own within a few days or as soon as people stopped. Only 8 of the 37 trials were rated good quality, and the authors wrote that the lack of long trials limits what anyone can say about continuous use. The US National Center for Complementary and Integrative Health also mentions a possible risk of allergic reactions.

Daytime sleepiness usually means the dose was too big or too late. The night curve shows why.

Does it stop working, or get habit-forming?

There’s no sign of either in the trials. In a 2013 analysis of 19 trials, the effect on sleep didn’t fade with continued use. In older insomniacs, two months of a nightly slow-release tablet kept working with no sign of tolerance, though their sleep got worse again when they stopped. And your own melatonin doesn’t switch off. In 21 night shift workers on 0.5 mg for a week, it came back at the same height. Does taking melatonin make your body stop making its own? has the details.

Which medicines does it interact with?

If you have epilepsy, use melatonin only under medical supervision too, since case reports suggest possible harm.

If you’re on blood pressure medicine and your prescriber agrees to a trial of melatonin, measuring at home for a week before and during it will show whether it moved your numbers.

What about alcohol?

It won’t undo a drink, and the drink works against it. In a 2007 study, 29 adults aged 21 to 25 drank vodka finished an hour before bed, a moderate dose. Their own melatonin was 15 percent lower than on a placebo about 2 hours later, and 19 percent lower about 3 hours later. Both alcohol and melatonin also make you drowsy.

On drinking nights, skip the tablet, and leave that night out of your two-week test. Drinks change your heart overnight too, and hrv.guide has what alcohol does to HRV.

Can I drive after taking it?

Don’t. In the 1994 MIT study, every dose from 0.1 to 10 mg made people sleepier and slower to catch signals on a listening test. That applies to the afternoon dose for moving your clock earlier as much as to a bedtime one.

What about pregnancy and breastfeeding?

There’s been a lack of research on melatonin’s safety in pregnancy and while breastfeeding, so we give no window and no dose.

The light steps need no pill. Keep a fixed wake time, get daylight in the morning and use dim lamps in the evening.

Is melatonin safe for children?

That’s a question for your child’s doctor, and we give no window and no dose for anyone under 18. The US National Center for Complementary and Integrative Health says parents should speak with a health care provider first. Nobody knows what dose to use in children or when, what long-term use does, or whether the benefits outweigh the risks. Because it’s a hormone, it’s possible it could affect development such as puberty, though that hasn’t been shown. The American Academy of Sleep Medicine has also issued a health advisory on melatonin use in children.

The bigger everyday risk is a child finding the jar. US poison centers got 260,435 reports of children and teens swallowing melatonin from 2012 to 2021, and the yearly number rose 530 percent. By 2021 it was 4.9 percent of all such reports for children, up from 0.6 percent in 2012. Most were accidents at home involving children 5 or younger, and 82.8 percent of the children had no symptoms. Of the 27,795 seen at a health facility, 4,097 were admitted to hospital and 287 needed intensive care. Most hospital stays involved teenagers who took too much on purpose. Five children needed a ventilator and two died, both under 2, though the data didn’t show whether melatonin caused those deaths.

Are there other people who should skip it?

• Older adults with dementia. The American Academy of Sleep Medicine’s 2015 guideline recommends against melatonin for them.
• People who snore loudly or stop breathing in their sleep. Loud snoring or stopped breathing can be a sign of sleep apnea, and melatonin doesn’t treat it. See a doctor about it first.
• Older adults in general should go low. Melatonin may stay active longer in older people and cause daytime drowsiness, so start at 0.3 to 0.5 mg.

Does melatonin cause heart failure?

That hasn’t been shown. In November 2025 the American Heart Association put out a news release about a study to be presented at its Scientific Sessions, and headlines followed.

The researchers looked at five years of health records for 130,828 adults with insomnia, from a large international database. Those with 12 months or more of melatonin recorded in their records went on to have heart failure more often: 4.6 percent against 2.7 percent. They were also hospitalized for heart failure more often, 19.0 percent against 6.6 percent, and died of any cause more often, 7.8 percent against 4.3 percent.

The same release lists the problems. The study was a conference abstract that hadn’t been peer reviewed, and the findings were preliminary. The database mixed countries where melatonin needs a prescription, like the UK, with countries where it doesn’t, like the US, so anyone buying it over the counter was counted in the no-melatonin group. The researchers had no information on how bad each person’s insomnia was or on psychiatric conditions, which could drive both melatonin use and heart risk. And it can’t show cause and effect.

In 2026 a look at US national survey data from 1999 to 2018 found melatonin users differed from non-users from the start, mostly in sleep trouble and depression, and recent use wasn’t significantly linked to heart disease or heart failure. Its authors said it doesn’t prove melatonin is safe either. Another 2026 paper described the heart failure finding as a single unpublished abstract that hadn’t been peer reviewed or independently checked.

Checked 2026-11-14: we found no peer-reviewed paper from the abstract’s authors. Does melatonin cause heart failure? goes through it in full.