Melatonin Side Effects Are Mostly Mild in the Short Term

Melatonin Side Effects

The common side effects of melatonin are headache, dizziness, nausea and sleepiness, and in short-term studies they were mild. The National Center for Complementary and Integrative Health (NCCIH) cites a 2015 review that found only these mild effects in adults, surgical patients and people in intensive care. NCCIH also says long-term side effects are unclear.

The UK's National Health Service (NHS) side-effect list adds a few more common ones:

• daytime drowsiness or tiredness
• stomach pain
• irritability or restlessness
• dry mouth, or dry and itchy skin
• pain in the arms or legs
• vivid dreams or night sweats

Serious reactions are rare, affecting fewer than 1 in 1,000 people, per the NHS. They include fainting, blurred vision, confusion, bleeding that will not stop, low mood and severe allergic reactions. Stop melatonin and get medical advice if any of these appear.

Morning grogginess is the side effect most people can fix themselves. A 2023 review of melatonin in older adults found that daytime sedation mostly follows daytime dosing and tends to clear when the timing changes. Move your dose to 30 to 60 minutes before bed, and lower it if the fog stays.

What the Melatonin and Heart Failure Study Showed

The study linked a year or more of prescribed melatonin to more heart failure in adults with chronic insomnia, but it was observational and not yet peer-reviewed. The American Heart Association (AHA) released the abstract on November 3, 2025, ahead of its Scientific Sessions in New Orleans. Researchers used five years of health records from TriNetX, a global network of anonymized patient data.

The team compared 65,414 adults with chronic insomnia who had melatonin in their records for at least a year with matched adults who did not. The groups were matched on 40 factors, including age, blood pressure and body mass index. Anyone with earlier heart failure or other sleep drug prescriptions was left out.

The AHA release lists the limits plainly. Melatonin is sold over the counter in the US, so many users in the comparison group probably took it without a record. The data also lacked insomnia severity, depression and anxiety, each of which could raise heart risk and melatonin use at the same time.

The lead author, Ekenedilichukwu Nnadi, said the study cannot prove cause and effect. Our news briefing on the melatonin heart failure study covers the release in more detail. If you have heart disease or several risk factors and take melatonin most nights, raise the finding at your next appointment.

Melatonin Drug Interactions

Melatonin interacts with blood thinners, several sedatives and some antidepressants, so check your medicine list before the first dose. NCCIH advises medical supervision for people taking blood thinners or living with epilepsy. The NHS interaction list names these medicines:

• warfarin
• sleeping pills such as zolpidem, zopiclone and zaleplon
• benzodiazepines such as temazepam and diazepam
• fluvoxamine and amitriptyline
• opioid painkillers such as codeine and morphine
• ibuprofen, naproxen and other anti-inflammatory painkillers
• estrogen in birth control pills and hormone therapy
• blood pressure medicines
• carbamazepine, cimetidine and some antibiotics

The older-adult review reports that in people taking warfarin, melatonin may raise the international normalized ratio (INR), a clotting test. Fluvoxamine can push melatonin levels 2.8 to 12 times higher. Taken with zolpidem, melatonin added to the sleeping pill's harm to driving and coordination.

Blood pressure can move too. In one study the review cites, 5 mg a day for four weeks raised blood pressure by 6.5/4.5 mmHg in people taking nifedipine. Ask your pharmacist to run an interaction check if you take any medicine on the list.

Melatonin in Pregnancy and Breastfeeding

Melatonin is not recommended in pregnancy because its effects on a developing baby are not well understood. NCCIH says research in pregnancy and breastfeeding is lacking. The NHS pregnancy guidance generally advises against it and asks you to tell your doctor if you become pregnant while taking it.

Breastfeeding is a closer call. The NHS says you may take melatonin while breastfeeding if your doctor confirms your baby is healthy, since only a small amount is thought to reach breast milk. Watch for a baby who seems unusually sleepy or feeds poorly, and do not share a bed with your baby while you take it.

Melatonin Side Effects in Children

Children usually have mild side effects from melatonin, but accidental overdoses have climbed fast. NCCIH lists drowsiness, bedwetting or more evening urination, headache, dizziness and agitation in children. It also notes that any effect on puberty or other hormone development is unknown.

A 2022 Centers for Disease Control and Prevention (CDC) report counted melatonin ingestions in children and teens rising from 8,337 in 2012 to 52,563 in 2021. Over that decade, 4,097 were hospitalized, 287 needed intensive care and 5 needed a breathing machine. Two children under age 2 died, though the data could not show whether melatonin caused those deaths.

A 2024 CDC report estimated about 10,930 emergency visits from 2019 to 2022 for unsupervised melatonin ingestion by children 5 and under. Gummies were the most common form, at 47.3% of those visits.

The label adds risk. A 2023 study in the Journal of the American Medical Association (JAMA) found gummies held 74% to 347% of their stated melatonin. Its authors estimated that a child taking them as directed could get 40 to 130 times the dose that raises nighttime levels in young adults.

The American Academy of Sleep Medicine (AASM) advisory asks parents to see a pediatric clinician before giving melatonin at all.

Is Taking Melatonin Every Day Bad?

Taking melatonin every day is reasonable for short courses, and unproven for months or years. The NHS usually prescribes it for 1 to 4 weeks, and up to 13 weeks unless a specialist advises longer, per its dosing guidance. Beyond that window, the only large signal on long-term safety is the unreviewed heart failure abstract.

Melatonin is also a weak fix for chronic insomnia. The AASM 2017 guideline suggests against melatonin for long-term insomnia, after trials of 2 mg cut the time to fall asleep by about 9 minutes. The American College of Physicians (ACP) recommends cognitive behavioral therapy for insomnia (CBT-I) as the first treatment instead.

Melatonin side effects are a poor fit for some people. Skip it, or get a clinician's sign-off first, if any of these apply:

• you are pregnant
• you take warfarin, fluvoxamine or a sedative
• you have epilepsy
• you are an older adult with dementia, a group the AASM advises against treating with melatonin

Our view would change in either direction with better data. A peer-reviewed study that confirms the heart signal would argue against nightly use, and one that finds no link after counting over-the-counter users would ease the concern.

Our insomnia guide walks through CBT-I and the medicines that come after it, and the sleep and recovery hub covers sleep apnea and other causes. If you keep using melatonin, set your dose with our melatonin dosage guide, or compare a non-hormone option in magnesium for sleep. Write down how many nights a week you take melatonin this month, and bring that number to your next checkup.