Is it safe

What are the side effects of melatonin?

By GyroscopeUpdated November 14, 20266 sources

Usually mild. Across 37 trials with doses from 0.15 to 12 mg a day, the most common were daytime sleepiness (in 1.66 percent of people), headache (0.74 percent), dizziness (0.74 percent) and a drop in body temperature (0.62 percent). Most went away on their own within a few days or when people stopped.

Melatonin feels harmless because your body makes it, and for most people in short trials it was. But a tablet can put far more in your blood than your body ever does, for far longer, and most of the side effects come from that.

We’d treat morning grogginess as a sign the dose was too big or too late, and fix it by going smaller and earlier. Anything beyond that, such as palpitations or a new medicine in the mix, is a question for a doctor.

Melatonin’s main side effect is its main effect at the wrong time, the way a strong coffee is great at 8am and a problem at midnight.

The side effects in the trials

A 2019 review pulled together 37 placebo-controlled trials of melatonin for sleep problems. Most lasted 4 weeks or less, the longest about 29 weeks.

A few people had effects the reviewers counted as more significant: agitation, tiredness, mood swings, nightmares, skin irritation and palpitations. None were life threatening. The US National Center for Complementary and Integrative Health also mentions a possible risk of allergic reactions.

Why sleepiness and a cold feeling top the list

Both are what melatonin does at night, carried into the day. In a 1994 study at MIT, every dose from 0.1 to 10 mg, given at 11:45am, made people sleepier, lowered their temperature and slowed them on a listening task that afternoon. In a 2001 trial of adults over 50, 3 mg at bedtime lowered body temperature and kept melatonin raised into daylight, while 0.3 mg didn’t linger. Small evening doses avoided the next-day effect. In a 1995 sleep lab test, 0.3 or 1 mg at 6, 8 or 9pm caused no hangover on the morning tests.

In the jet lag trials, melatonin taken early in the day made people sleepy and slowed their adjustment.

Who should be more careful

• People on daily medicines. Melatonin interacts with some, including fluvoxamine, blood thinners and nifedipine. See the medicines answer.
• People with epilepsy. Case reports suggest possible harm, and the NCCIH says people with epilepsy need medical supervision.
• Older adults. Melatonin may stay active longer and cause daytime drowsiness. Start at 0.3 to 0.5 mg, as the older adults answer explains.
• Pregnancy, breastfeeding and children. There’s not enough safety research, so start with the pregnancy answer or the children’s answer.

What isn’t known

Nobody knows much about the long run. With most trials at 4 weeks or less, the reviewers said there isn’t enough long-term evidence to judge continuous use over years. Can you take melatonin every night? covers what that means for a nightly habit, and the heart answer covers the 2025 heart failure headline.

Don’t drive after a dose.