Has anyone experienced diarrhea with Melatonin use?

We stopped the melatonin on Monday 3/22/21. My wife had 4 explosive liquid events between 7:30 and 11:30 AM on Tues and Wed, one event Thurs at 7:30 AM, followed by a soft but formed stool at 1:00 PM, and a small liquid event at 7:30 AM today, with no follow-up so far (2:30 PM).
Trying to understand why some people ( 0.1% of the population?) might experience diarrhea as an “adverse event” (AE) from melatonin supplementation, I read about 80 abstracts and 27 entire published papers dating from 1998 through 2021.
Findings:
- Serotonin is a melatonin precursor. LabCorp gives a Lab Ref Range (LRR) of 21 – 321 ng/ml for males and 0 – 420 ng/ml for females. Other sources give narrower ranges (50-200, 100-280, <330) w/o the gender distinction. (My wife’s average level over several years is 3x my level and in the upper 3SD range of the LabCorp ref range).
- Folate and Vit B6 promote serotonin production. Many multivitamins and B-Complex supplements contain levels of these 2 vitamins that are up to 2x the recommended daily allowance for folate and 60x for Vit B6.
- Serotonin is found in the stomach and intestines. It helps control bowel movements and digestive function.
- Conversion of serotonin to melatonin is subject to very wide variation due to genetic SNPs.
- Endogenous melatonin production in subjects w/o supplementation varies from 2 – 84 pg/ml, - 40:1!
- There are large inter-individual variations in bioavailability of exogenous melatonin (1% to 37%) – median level 3x as high in females as in males.
- For sleep a dose of 0.3 mg/day is better than 0.1 mg or 3.0 mg.
- Peak concentration of melatonin after supplementation is proportional to dosage and subject to very wide inter-individual variations: 0.1 mg dose peak median is 5x baseline, - range of 2x-7x
- 0.3 mg dose “ “ is 10x “ “ of 5x – 15x
- 0.5 mg dose “ “ is 25x “ “ of 20x – 30x
- 3.0 mg dose “ “ is 600 “ “ of 300x – 1000x
- A 5 mg dose for 30 days raises the mean baseline level by 2.5x.
- 37 Randomized Controlled Trials (RCTs) with doses from 0.5 mg to 12 mg and followed for up to 29 weeks had levels of adverse events less than 2%, none of which were diarrhea, and none of which were clinically serious.
- High levels of serotonin can lead to “serotonin syndrome” which can be fatal, and has numerous symptoms including diarrhea.
It seems likely that a very small %age of people that are at the high end of peak concentration response to dosage, probably due to genetic variants, and/or that have elevated levels of serotonin, elevated levels of B vitamin supplementation, high levels of endogenous melatonin, and are female may have a particular sensitivity to supplemental melatonin that leads to diarrhea. It seems that the %age is low enough to have escaped detection in scientific trials. Some of them might get the benefits of melatonin supplementation at very low dosage - =< 0.3 mg.
Medical science is clearly unaware of this issue, and has not even seen all of the dots, let alone connecting them.

Post Edited (murrayv) : 4/2/2021 1:11:29 PM (GMT-6)

I too had a visit from the diarrhea monster after taking 10mg of gummy melatonin. A few weeks ago I had a bad case of diarrhea. I had been taking melatonin for a couple of weeks initially with no bad side affects. Suddenly wam I was hit hard with diarrhea that lasted a week before I had remembered a cure for chronic diarrhea issues. I was told 20 years ago by a doctor to give my bowels a “rest” for 3 days by having just clear liquids. This cured my diarrhea. I had also stopped taking the melatonin at the same time. Well I did this again recently not knowing I could have just stopped taking the melatonin. The good thing about the 3 day fast is you’re cured faster then if you just stop taking the melatonin which others in this chat say takes 3 weeks on average to stop the diarrhea. So anyone out there having diarrhea after taking melatonin FIRST STOP TAKING MELATONIN and then I recommend the 3 day fast rather then suffering 3 weeks. Then take probiotics to put the good guys back in your system. Good luck, I feel for anyone going through this.

I too am joining the club - out of gratitude to those of you who started this forum, as i was so worried about this new problem of diarrhea i was having and thankful to find you! yes, i had been on melatonin for 3 months for sleep help then the big (S*)IT started. after reading your forum posts, i stopped melatonin and assumed i would be soon healed. 12 weeks later and NO healing! i started doing research, and on dr. axe website he mentioned the amino acid l-lysine for diarrhea. i started it 36 hours ago and this morning was first firm stool in 12 weeks! i am taking jarrow brand l-lysine 500 mg pill, one pill 40 minutes before eating, 4 times a day (=4 pills per day). its only been one day so i hope this continues working! additionally it seems to have helped with anxiety too. godspeed all.

Me too! What has been shared about Melatonin. I had worries, concerns as have been described in the posts, I took myself to Urgent Care as my regular doctor was not available.and 3 weeks of irregularities (nice way to talk about this New Symptom of explosive, serious diarrhea), Obviously the doctor at Urgent Care couldn't do much in way of testing, which is fine as I have turned down a few of those tests when my regular doctor wanted me to do them. The doctor at Urgent Care did suggest digestive difficulties, with a bug and starving the bug by eating only the BRAT diet. So that is what I did yesterday, had no appetite anyway. This morning ate nothing, not water, not morning coffee, not anything at all. And....yep, you guessed it, mean, messy, diarrhea. I had taken the Melatonin the night before.
It WAS the Melatonin pills! Had to be, so that does it for me. No more Melatonin even if it does help with sleep considerably. I am diabetic 2, which was dx in 2018, and I immediately changed my diet, lost weight, exercised and we have been homebound the past year (Covid) so had developed regular plans with food, exercise, etc.. Trying to eliminate the cause of the diarrhea and went looking online for Melatonin side effects to which there is No Reference to Melatonin causing this new to me symptom. Wow! Yes, physicians would well benefit in knowing about this side effect as it is mainstream in my daily life! I will give some time to the stopping of Melatonin, see when the diarrhea clears, and add another post.
Thankful to the people who posted at this and there are 5 pages with pretty much same stories about side effects unknowing, dr visits and the mental concern of 'What Does This Mean'......

Thank goodness I found this forum. I had been taking 3 mg melatonin post covid for sleep and to help with tinnitus for 3 or 4 months. 2 weeks ago I had the explosive watery diahorrea 6 or 7 times a day, took me a week to realise it may be the melatonin. I stopped 8 days ago and no let up with the diahorrea , I’m scared this will never stop. I can’t go walking like normal , every time I eat I run to the loo, if I don’t eat I feel weak. Please tell me this will eventually stop m I’m not seeing improvement after 8 days 😔

Wendyb68 said...
Please tell me this will eventually stop m I’m not seeing improvement after 8 days 😔

A few pages back, someone suggested a clear liquid diet for three days. I tried that, and the cramps stopped immediately. It took about three weeks for the diarrhea to stop altogether, but it did stop.

Mello2021 said...


I have been controlling melatonin diarrhea with Imodium. Usually 2 tablets work, but now must take 4 to 6 per day. Still trying to find right dose for chronic insomnia. Stopped Rx used since 1972. Any suggestions?

Imodium totally failed for me, and it had always worked before. My GP prescribed Lomotil, which allowed me to function. I would rather deal with insomnia than try melatonin as I was taking the smallest dosage available, so I have no suggestions for insomnia.

I started melatonin around 10 weeks ago 4mg increasing to 6mg, chronic diarrhoea started soon after, I read the side effects leaflet and nothing was mentioned so thought it was something else, I’ve had numerous tests, blood, stool and a colonoscopy all in the past 6 weeks. As I was worse on a morning I started to suspect my meds, and googled melatonin and diarrhoea and I found loads of info, including a paper that was completed about melatonin and how it helped to get it removed from health food shops in high doses as it causes adverse reactions in some people. So I have now stopped melatonin and I am so much better, I didn’t get woken up needing to rush to the toilet for the 1st time in 10 weeks. My doctor who prescribed this for me was also running all the tests on me due to chronic diarrhoea so obviously was unaware this drug can cause this issue.

I took melatonin for about a year with more and more diarrhea, hair lost, 10-15 completely liquid bowel movements a day, cramping, bloating, severe pain, I couldn't lose weight etc. No md ever suggested the problems could be from melatonin. Finally I came across this site and stopped the melatonin. I finally found this thread in March of 2021 and stopped the melatonin. It has taken me several months to stop the diarrhea and it is not completely back to normal yet but I am much much better (but I did have diarrhea for almost a year so I think I just have a lot of it in my body). I felt like I was going crazy. All the stool samples and scans came back negative but it was horrible and the mds didn't really have any ideas except more tests/colonoscopies etc. I am feeling so much better now that I stopped taking it and glad I didn't go through some of the medical tests they were advising.

Post Edited (topperspot2222) : 9/23/2021 9:02:18 PM (GMT-6)

I am so thankful I found this site. about 4 years ago I was doing my hormone panel (urine test for hormone levels) and it measures melatonin. My doctor told me that my melatonin was very low and that low melatonin puts you at risk for cancer. I started melatonin and like most people on this thread did not associate the melatonin with my urgent diarrhea that was 10-15 times per day. I could not even leave the house. I also went to a gastroenterologist and had all the tests done and a colonoscopy. I scoured over everything I was doing and what I was eating. I was taking a very low dose of melatonin (1 mg) but it was the only thing that had changed. I stopped it and continued with stomach issues for more than a month. Fast forward to my next doctor physical/tests and he once again said my melatonin was low. I told him about my stomach issues and he said that melatonin was not the problem and had never heard of that. He recommended trying melatonin in a sublingual form. I tried it and had the same issue and again suffered for another month. My husband and daughters all take melatonin daily and have never had any issues. This year, my physical once again comes around and he is discussing the melatonin. I tell him that I am convinced that it is the melatonin that caused me so many stomach issues and he once again says there is no merit to my claims. He tells me that there is so much research now about how great melatonin is and how they are finding it is very good for fighting off covid and using in the treatment of Covid. I relay to him that when my elderly mother (86) was hospitalized for covid, the hospital gave her melatonin nightly and was in her notes to continue after release. I agree that melatonin does appear to be a great supplement but maybe my body just doesn't tolerate it. I told him that I researched and found that tart cherry contains melatonin so I was taking that instead (no stomach issues at all from this). He said that was good but that I should again try the melatonin. I ordered a liquid melatonin because he suggested if I bypassed the swallowing of a pill it may ease any stomach issues I thought I was having. I have taken the melatonin for 2 nights. Today I have been to the bathroom 3 times and have stomach cramping. This is not in my head and have been to a gastroenterologist all 3 times I took melatonin thinking I had IBS-D. I am done with the melatonin and will continue my tart cherry path and make peace with my low melatonin levels and cancer risk.

I created an account just to reply to this thread (like a lot of others!)

I experience these issues as well with most dosages of Melatonin. It's ALMOST worth it, so long as you work from home are near a bathroom the entire day! I don't have cramping until right before I have to go, but I had better go when the call comes or else.

I spent a month ruling out everything BUT melatonin, and about 48hr after stopping melatonin, all my problems went away. Taking 5mg at night before bed results in the next 24hr of very loose bowels.

I've found that taking the 300mcg dose of melatonin earlier in the day provides many of same benefits as taking 5mg 30 minutes before bed. See: https://slatestarcodex.com/2018/07/10/melatonin-much-more-than-you-wanted-to-know/

Chiming in like others in hopes to help people who find there way to this topic. I started taking melatonin months ago. No problems at first and then every morning diarrhea began and occasionally in the evening. I'm an intermittent faster and eat one meal most days. Otherwise, I'm sure I would have been running to the bathroom all day! I had IBS-C years ago but this was different. I tried everything! Parasite cleanse, colostrum, probiotics, acacia fiber. I'm in menopause. Was it hormonal? Did I unknowingly have Covid at some point and I'm now a long hauler? Do I have colon cancer? Is it my gallbladder? I drove myself nearly out of my mind! Never once did I think it was melatonin. I'd forget to take it on occasion, still diarrhea so it just didn't register. And then thank you Google I found this forum. Immediately stopped melatonin and now one day shy of two weeks, normal bowel movements. It's a miracle and a huge weight off of my mind. I wish this side effect was easier to find information on. I am getting a colonoscopy next month that I needed to do anyway. I'm considering telling them this story. I'm so happy!

Post Edited (TeeAnn) : 2/28/2022 6:46:25 AM (GMT-7)

Update- it took 2 weeks for me to feel better!!!!