Melatonin Side Effects: Why It’s Not As Safe As You Think

Melatonin is one of the most popular sleep aids on the planet. But despite it’s widespread use, it may not be as safe as you think.

While it definitely does it’s job - there are some major undisclosed downsides that make this very common supplement - very concerning.

Here’s why melatonin might not be as safe as you think it is.

What Is Melatonin

Melatonin is a hormone found naturally in the body and a sythentic form found in a supplement that’s usually available in pill form.

It’s often used to treat insomnia and poor sleep - especially with jet lag or shift workers, but there are some specific reasons why we recommend you stay away from melatonin for these uses.

(Melatonin Diagram coming soon)

What makes Melatonin Uniquely Dangerous

Melatonin is different from other sleep compounds because it’s a hormone that your body naturally produces rather than a mineral your body needs supplemented.


Taking exogenous hormones can actually make your body less likely to produce that hormone.

We know this already when people take exogenous hormones like testosterone or estrogen that your body down-regulates itself and produces less to achieve a more equilibrium state.


A similar effect is seen with melatonin - exogenously supplementing it actually can diminish your body’s ability to produce it! Not good!

What Are The Side Effects of Melatonin?

Because melatonin specifically affects your brain, the common side effects include:

  • Headache
  • Dizziness
  • Nausea
  • Drowsiness

That last one is expected for a sleep supplement (but if you’re taking melatonin away from home when you should be alert - it may cause other issues).

Supra-physiological Dosages of Melatonin

Melatonin is produced naturally by your body every day - with your melatonin levels peaking mid-sleep.

However, your body only produces a small amount. According to a study:

the average daytime and peak night time values are 10 and 60 pg per millilitre (40 and 260 pmol per liter), respectively.

That’s .000 000 26 Milligram per milliliter (mg/ml). Not a lot of melatonin.

Most sleep supplements contain 1-10mg of melatonin. This is absolutely astronomical amounts.

That means, on average you’re taking 10x-100x the amount of peak melatonin you’d naturally produce at peak night time an hour before you actually go to sleep.

Not only is that concerning, but it can affect your hormone profile quite drastically (more on that in a moment).

Melatonin + Medication Interactions

According to the Mayo Clinic, Melatonin has been known to interact poorly with the following drugs:

  • Anti-caogulaants
  • Blood pressure medications
  • Central nervous system depressants
  • Diabetes medications
  • Contraceptive drugs
  • SSRIs + other similar medications0
  • Immunosuppressants
  • Seizure-specific medication

Because of the wide array of interactions with common prescription drugs, many people can take melatonin without knowing the bad and sometime dangerous side effects that can come from mixing it with particular prescriptions.

Unique Risks of Melatonin

There are a couple specific unique risks of melatonin.

Hormonal modulation + dependency (especially in teens).

Melatonin is uniquely dangerous again because it’s hormone modulation - not a mineral or supplement.

As Andrew Huberman explains:

The melatonin system is closely linked up with GABA inhibitory neurons in the hypothalamus. It effectively keeps puberty from happening. So the melatonin rhythms of young children, pre-pubertal children, are not as phasic, right? They’re pretty constant. And that’s one of the reasons they don’t go into puberty.


He goes on to mention.

we were working on these little, they’re called Siberian hamsters, these little hamsters, who in long days, because they are seasonally breeding animals, in long days, these Siberian hamsters have testicles, well, that at least for Siberian hamsters, are a pretty impressive size. If however, you inject those animals with melatonin, or you put them into short days, so you increase the amount of darkness and you decrease the amount of light, remembering, of course, that light inhibits melatonin, their testicles shrink to the size of a grain of rice….. And it turns out in females of the same species, they leave estrous, they stop cycling. They don’t have menstrual cycles, they have estrous cycles. And there are powerful effects of melatonin on the reproductive axis.

Hormonal modulation + dependency.

Because melatonin is a hormone produced by the body instead of a mineral or compound you typically ingest, taking exogenous hormones can interfere with your body’s natural production.

We see this clearly when people take exogenous hormones like testosterone or estrogen - that they interfere with your body’s natural production of those hormones. The same is similar to melatonin as increased use over time can lead to needing higher dosages to get the same level of rest or seeing the body down-regular your natural melatonin production now that you’ve introduced exogenous supplementation.

Who Should Avoid Melatonin

There are several groups that should consider avoiding melatonin.

  • People taking interfering medications
  • Young children who simply have a hard time sleeping.
  • People with chronic insomnia. Insomnia is a much bigger issue than simple melatonin supplementation can solve. If you suffer from this - please see a doctor.
  • People with restless leg syndrome. Melatonin can sometimes interfere or make this worse.
  • People with dementia. Because dementia can cause people to metabolize the hormone more slowly - they may become drowsy during the daytime and pose a danger to themselves.

What Should You Use Instead?

We recommend you stay far away from melatonin as a sleep supplement for the reasons listed above. It’s popular for a reason (it does work), but has side effects that most companies do not talk about and do not disclose.


The interactions with children concern us the most, but anything that can affect or reduce your natural hormonal production is worrisome and worth avoiding if you don’t absolutely need it.

If you’re interested in trying other sleep solutions, consider the following:

  • Magnesium (particularly magnesium l-threonate)
  • L-theanine
  • Chamomile tea

After struggling with sleep and restlessness a long time, we sat down and put together a perfect formula designed to act fast, help you recover and ‘turn off your brain’ when it comes time for bed.

It also taste delicious, is 100% natural and won’t build dependencies. It’s called Impossible Sleep - try it out here.

Melatonin Citations + References

Other resources + references on melatonin & sleep:

Photo by Alexandra Gorn on Unsplash

About Joel Runyon

Joel Runyon

Joel Runyon is the founder of IMPOSSIBLE. Building off his impossible list, IMPOSSIBLE has grown into a blog, a fitness training site, a philanthropy initiative, along with Impossible.co - an e-commerce branch focused on performance apparel and supplements.