Answer:

Melatonin supplements, taken in low to moderate doses (0.3 mg to 3 mg per day) for short-term use, are generally safe and well-tolerated. The most commonly reported side effect is drowsiness, followed by headache and dizziness. Drowsiness and impaired mental alertness and balance may occur for about six hours after taking melatonin (these effects may last longer or carry over into the next morning if taking controlled-release, higher dose products). Moderate to very high doses of melatonin have been reported to affect mood and behavior is some people. 

Melatonin should not be taken long-term, but only as needed for limited periods of time. Long-term use has been associated with increased risk of fractures in older adults, possibly due to an effect on bone metabolism. Melatonin can may also affect blood pressure, aggressiveness, blood clotting, seizure activity, and, at very high doses, ovulation, depression, and schizophrenia. For details, see the Concerns and Cautions section of the Melatonin Supplements Review (which includes our Top Picks among products).

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13 Comments

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Margaret18763
December 23, 2019

Several years ago my husband was taking melatonin for better sleep. At bedtime, he was taking melatonin for immediate release, plus a time-release melatonin. He also usually ate a bowl of cherries (which is high in melatonin). This was taking care of his sleep issues, but now he does not take melatonin at all. He was/is on Eliquis blood thinner and he had a terrible internal bleed that nearly took his life. After many tests, the cause was never found, but due to even a remote possibility of melatonin being a factor, he no longer takes it.

robert18758
December 22, 2019

I get itchy when I take melatonin

peter18317
September 10, 2019

I'm a pharmacist ,and in my opinion melatonin is 1000 times better than taking most prescription sleeping pills that shorten your life , and are addictive .I always recommended no more than 3 mg.

Jay18312
September 8, 2019

Melatonin can cause a gassy diarrhea. This is especially pernicious because people often do not realize the cause and continue to take melatonin which makes the problem worse.
See, for example, a case report here: https://www.researchgate.net/publication/272100573_Melatonin_as_a_probable_cause_of_diarrhea/link/591efd53458515405963c109/download
Personal accounts here:
https://www.healingwell.com/community/default.aspx?f=26&m=2994343

RUTH18083
June 27, 2019

I read about a small study where PCOS sufferers reduced their testosterone levels and increased their cycles by taking 2mg. a day for six months. My nineteen year old is trying it. Are there any health concerns with long term use?

ConsumerLab.com
June 27, 2019

Hi Ruth - As noted in the answer above, melatonin should only be taken as needed for limited periods of time, and there is concern that long-term use may increase the risk of fractures. More information can be found in the "Concerns and Cautions" section of the Melatonin Supplements Review: https://www.consumerlab.com/reviews/melatonin-supplements/melatonin/#cautions

John17502
January 28, 2019

I have been taking melatonin for some years, and have found the following works for me:

1) "Less is more" - 0.5 mg. (500 mcg.) works better than larger doses. It is sometimes difficult to find that dosage -- right now I am splitting 1 mg. tablets in half.

2) I try and take my dose only once at bedtime. I have found that if I take it to go back to sleep after waking up too early, say 4:00 AM, I am groggy the next day.

3) Melatonin does not act quickly like sleeping medication. It helps initiate your brains natural sleep cycle. For me it takes 1/2-1 hour to fall asleep, but then I have a good sleep.

4)I found at one time I was getting dependent on melatonin to fall asleep. Not in an addictive sense, but psychologically I became anxious that I wouldn't be able to sleep without it. So I try and use it only when I am having trouble falling asleep naturally, as when I have had caffeine too late or didn't get enough physical exercise.

susan 17206
October 1, 2018

I take 0.5mg when i travel, to deal with Jetlag. It works well. I don't chew or swallow, i let it dissolve under my tongue. Trader Joe's brand works best. The high doses people mention here as 'low' don't surprise me as having weird effects. Stay low, it works better.

Satu17203
September 30, 2018

I'm a woman 70 yrs, I take melatonin every evening 3 mg. I don't find any problem with it.
This is something speciaI want to tell:
I know a person who had been drinking lots of alcohol and taking all kinds of drugs,
many many years. Finally she got sober but insomnia was a bad problem. You can trust the doctors don't easily give prescription sleeping drugs to such a person but she really could not sleep at all without quite heavy medicins. Then she tried melatonin; if I hadn't seen it myself maybe I wouldn't believe that this natural and mild stuff helped her. She was able to stop taking heavy sleeping drugs, and she says her dreams are nice and sweet, no nightmares any more. - I just wanted to tell this. Maybe it's a sign how different all the people are.

Rebecca16943
July 5, 2018

Melatonin makes my eyes very glassy for up to 18 hours after I take it. Even taking a dose as small as 1.5 mg causes this problem.

Sheryl16942
July 4, 2018

I tried a low dose of Melatonin a few times and every time I had nightmares. I mentioned this to a friend and she had the same experience.

Idy18757
December 22, 2019

For me, even very low dose of melatonin gives me awful nightmares & huge head ache. My sisters have had the same experience.

Judith16940
July 4, 2018

In response to Robert's comment about melatonin making him feel jittery, I have restless legs syndrome, and I have noticed that just 2 mg. of melatonin will bring on the jittery need to move characteristic of this disorder. The Restless Legs Syndrome Foundation's medical bulletin mentions melatonin, along with other over the counter medications like antihistamines, as a substance that aggravates RLS symptoms. It would be helpful for the four percent or so of us that have this condition if you would mention this possible side effect of melatonin.

ConsumerLab.com
August 8, 2018

Hi Judith - Thank you for sharing this. The "Concerns and Cautions" section of the Melatonin Review discusses the effects of melatonin in people with restless legs syndrome: https://www.consumerlab.com/reviews/melatonin-supplements/melatonin/#rls

Robert16936
July 4, 2018

Melatonin makes me feel agitated, even in small doses.
A good friends has the same reaction, as does my son.
I'm surprised not to see mention of this possible side effect.

ConsumerLab.com
July 4, 2018

Hi Robert - Thank you for sharing your experience and your son's experience with this. Although as noted in the answer above, changes in mood have typically been reported at higher doses, one study reported increased "reactive aggression" in young men given a more typical dose. This is discussed in the Concerns and Cautions section of the Review: https://www.consumerlab.com/reviews/melatonin-supplements/melatonin/#aggression

Isabel16578
March 14, 2018

I have found that VERY low dose melatonin (300 mcg - that's 0.3 mg) works better than any of the higher doses I've tried, which were 1 mg, 2 mg, and 5 mg.

But what has worked better still, in the two weeks I've been using it, is Dream Support for Women (I'm a woman) from weilvitaminadvisor.com. This contains vervain, California poppy, valerian, and ashwagandha. This combination is said to be "evidence-based" and Dr. Andrew Weil is someone I trust - his books are thoughtful, and he got his M.D. from Harvard Medical School.

Unfortunately it also contains 125 mg calcium citrate (with 62.5 mg of magnesium) and I've been reading lately that calcium in pill form can cause problems if taken long term. It's better to get it from diet. My next project is to look for the three herbs without the calcium. I will look at Mountain Rose Herbs and Jean's Greens to see what they have.

ConsumerLab.com
March 15, 2018

Thank you for sharing this Isabel. You may be interested in the CL Answer about getting calcium from supplements: https://www.consumerlab.com/answers/how-much-calcium-is-too-much/how_much_calcium_is_too_much/

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