Are there negative effects of melatonin?

Melatonin is a hormone that your body uses naturally to regulate when you sleep.

Darkness causes your body to produce more melatonin, and light causes a decrease.¹

However, some people may have low levels of melatonin, for a variety of reasons, including old age, stress, a disrupted sleep schedule (for example jet lag or working shifts), and more.

Laboratories can produce this hormone so that you can then take it, if you need more – particularly to combat insomnia.²

People also may take melatonin to help relieve headaches, or even as part of a broader strategy to lose weight.

How to take melatonin

The most common way to consume melatonin is in pill form, though you can also get it in forms that allow you to place it in your inside cheek or under your tongue, so that it can be absorbed more directly, and act more quickly.³

For tablets however, they do take an hour or so to work, so they should be taken about an hour before you hope to sleep.

In terms of dosage, it is worthwhile having a chat with your doctor, if you can. However, generally, the following doses have been studied in scientific research.

Blind people have taken such doses for up to six years.⁴

Melatonin for sleep

If you have delayed sleep phase syndrome, where you struggle to fall asleep and/or wake-up at conventional times, you can take 0.3 to 5 mg of melatonin daily for up to nine months.

Similarly, for insomnia, two to three mg are typically recommended for up to six months, or higher doses could be taken for a shorter period of time.⁵

For jet lag, you can take 0.5 to eight mg of melatonin at the new location’s bedtime, after you arrive, and maintain that for two to five days.⁶

Possible side effects of melatonin tablets

Melatonin tablets are likely safe when used in the short term, and possibly safe in the long term.⁷

The most important thing is to understand that the hormone causes drowsiness, so do not drive or use machinery or start a long work meeting for four or five hours after taking it.

Some potential side effects that a few people may experience after taking melatonin include feelings of depression, daytime sleepiness, dizziness, irritability, or stomach cramps.⁸

If you get one or more of these side effects, they are typically experienced in a mild way, only.⁹

Melatonin’s impact on people who are pregnant or breast-feeding has not been sufficiently studied in order to be able to categorically say that it is safe in those cases.¹⁰

Because melatonin causes you to feel sleepy, it should not be taken with any other sedative medications.

Melatonin could also have some interaction with birth control pills, since these too seem to increase how much melatonin the body makes.

Caffeine can decrease your melatonin levels, so if you drink coffee, for example, while taking melatonin supplements, they may not work.¹¹

Melatonin side effects and risk

When consuming most supplements and medicines, a few side effects are possible.

However, unless otherwise indicated, “possible,” does not mean such effects are at all likely.

For example, if a side effect is described as common, it means it only effects one in 10 to one in 100 people, and if it is described as uncommon, it will affect between one in 100 and one in 1,000 people.¹²

For example, headaches are common when taking melatonin, but you still have less than a 10% chance of getting one.

Dizziness, abdominal pain, and nausea are uncommon, so you have less than a 1% chance of those side effects.¹³

The chance of side effects happening does increase if you take too much of the supplement or medicine, or if you use it in the wrong way, or in conjunction with other medicines or remedies.¹⁴

If you get a mild side effect, you then have a choice as to whether or not the side effect is worth the benefits of taking the supplement or medicine.

If you do not consider that it is worth it, you can usually stop taking the medicine and then consult with a professional about alternatives.

In the case of melatonin, there are no problems with stopping it when you want to.

Do seek help though if you think you have had a serious allergic reaction to a medicine, or see a general practitioner if you experience a side effect that you think is severe.¹⁵

Last updated: 17 March 2021