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Can you overdose on melatonin?

Written by Florrie Byrd

If you’ve ever gone through a bout of insomnia, you probably have a bottle of melatonin sitting in your medicine cabinet. It’s available without a prescription, it’s inexpensive, and some studies suggest that it can be an effective sleep aid for some people.

But how much should you take? The truth is, probably a lot less than you think. And while there’s no evidence that taking large doses of melatonin can be life-threatening, it can definitely cause unwanted side effects. And taking too much melatonin on a regular basis can cause rebound insomnia, meaning not only doesn’t the melatonin work anymore, but it can actually make your sleep problems worse.

So the short answer to the question is, no, you can’t overdose on melatonin. But you can have some very unpleasant side effects if you take too much.

What’s the correct dose of melatonin?

There’s a lot of variation in what is considered a healthy dose of melatonin, and how much you should take depends on your age, how healthy you are, and what you’re using it for. If you’re taking it for insomnia, to adjust your circadian rhythm, or to combat jet lag, the standard dose for adults is anywhere from .3 milligrams to 5 milligrams. The problem is that many melatonin supplements can have 10 times that amount in just one pill.

Another thing to think about: Because melatonin is considered a dietary supplement, it isn’t as strictly regulated by the FDA as prescription and over-the-counter drugs. So there’s no way to be sure that you’re actually getting what the label says you’re getting. A study that analyzed the melatonin content in 31 melatonin supplements purchased at pharmacies and grocery stores found that 70 percent of the supplements tested had more or less melatonin than what was advertised. One chewable melatonin tablet labeled as 1.5 milligrams actually contained almost 9 milligrams. That’s a little scary — especially if you’re thinking about giving melatonin to a child. Some experts suggest buying pharmaceutical-grade melatonin online, as the dosage is likely to be more reliable.

Melatonin safety tips

If you’re using melatonin for the first time, it’s always a good idea to start out at the lowest dose and work your way up in .5 milligram increments until you find the dose that works for you. You may find that .3 milligrams is all it takes to improve your sleep. Because melatonin doesn’t go to work as quickly as prescription sleep aids, you’ll need to take it at least an hour before you want to go to bed. And don’t expect the effects to be as pronounced — it might not make you feel very drowsy, but that doesn’t mean it’s not working.

One advantage of melatonin over other sleep aids is that when taken correctly, it doesn’t cause “sleep inertia” — that groggy, hungover feeling you sometimes get the day after you’ve taken a sleep aid.

Signs you’ve taken too much melatonin

As mentioned above, there haven’t been any reported cases of people dying — or even getting seriously ill — from an overdose of melatonin. But it can have some nasty side effects if you take too much.

Side effects from a too-large dose of melatonin include:

  • Daytime grogginess
  • Depression
  • Headaches
  • Hypothermia (low body temperature)
  • Stomach cramps
  • Irritability

In men, using too much melatonin on a regular basis may decrease libido and lower sperm count. In women, large doses of melatonin can affect reproductive hormone levels, including estrogen and progesterone. While there hasn’t been much research on the topic, there are some concerns that melatonin use may interfere with menstrual cycles and ovulation. If you’re pregnant or trying to get pregnant, talk to your doctor before taking melatonin.

Can melatonin interact with other substances?

It’s also a good idea to talk to your doctor before starting melatonin if you’re taking any prescription medications.

The following list of medications may interact negatively with melatonin:

  • Blood-thinning medications (anticoagulants): Melatonin may increase risk of bleeding.
  • Blood pressure drugs: Melatonin may make them less effective.
  • Diabetes medications: Melatonin may affect blood sugar and make these drugs less effective.
  • Birth control pills: Hormonal contraceptives increase your body’s natural levels of melatonin, so adding more may cause drowsiness.
  • Steroids and immune-suppressing drugs: Melatonin may make these medications less effective. Do not take melatonin with corticosteroids or other immunosuppressants.
  • Medications to prevent seizures (anticonvulsants): Melatonin might make them less effective, increasing the risk of seizures in some people.

Because melatonin has a sedative effect, it may not be a good idea to take it with other things that can make you sleepy, such as opioid painkillers, anti-anxiety medications, or alcohol.

Is melatonin habit-forming?

One upside to using melatonin is that you’re not likely to become dependent on it, which can happen with prescription sleep aids. However, taking high doses for a long period of time can have the opposite of the desired effect — it will keep you up instead of helping you sleep.

Is melatonin safe for children?

A lot of parents turn to melatonin when their child is having trouble sleeping. But how safe and effective is it really?

Studies have found that melatonin can shorten the time it takes to fall asleep in children with sleep problems — especially children with ADHD, autism, and other neurological disorders. However, there isn’t much evidence that melatonin is helpful for children who wake in the night and can’t get back to sleep.

And melatonin isn’t the best strategy if your child’s sleep problems are situational — i.e. caused by something that’s happening in their life — and haven’t been going on for very long. In these cases, it’s best to start with behavioral changes before you try melatonin.

While it seems not to have any short-term health risks, there just hasn’t been enough research of melatonin use in children to determine whether it has any long-term health risks. Some animal studies suggest that melatonin may delay puberty. While there’s currently no evidence that the same thing can happen in human children, we can’t rule out the possibility until more studies have been done.

Before you give your child melatonin, it’s a good idea to make an appointment with their pediatrician to make sure their sleep problems aren’t being caused by illness (like an ear infection) or some other underlying health issue (like sleep apnea). And before using melatonin, first take a look at your child’s bedtime habits. Sometimes a few small tweaks to the bedtime routine can make a big difference.

The bottom line

If you use melatonin to help you sleep, you can rest assured that even if you take way too much, it isn’t going to kill you (although you’ll probably regret it the next day). It’s generally safe for short-term use, non-habit-forming, and studies show that it does have some benefit as a sleep aid. But as with any medication or supplement, it’s best to take the smallest dose that’s effective for you to minimize side effects. And if you have a health condition or are taking prescription medications, you should talk to your doctor before you start taking it.

Additional Resources

Melatonin and Sleep
10 Tips to Help You Fall Asleep Faster