Will Melatonin Reduce Your Testosterone Levels? A Review of the Existing Evidence With Clinical Studies That Say...

Do you risk all of these benefits of T that have been illustrated artistically by artofmanliness.com if you take melatonin supplements?
I have written about the multitude of beneficial health effects which range from improvements in sleep quality over its beneficial effects on glucose and lipid metabolism to its potential cancer protective effects more than once; and after the publication of each of these articles I have received messages of some of you who were concerned that taking melatonin could ruin their testosterone levels.

Since interesting studies are a bit rare, these days I am going to use this article to address this issue once and for all: There is no conclusive evidence that melatonin could put you at risk of developing full blown hypogonadism (=clinically low T).
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In fact, only a few days ago, researchers from the International Centre for Agricultural Research in the Dry Areas in Jemen published a paper the results of which directly refute the studies some of you have been throwing at me to "prove" that what some kind of guru told you about the effects of melatonin on testosterone was true.

In the previously mentioned study, Rekik et al. tested the effect of melatonin treatment, initiated in late February on reproductive traits of young rams. Yes, that's male rodents, but the study by Yilmaz et al. which shows an inhibitory effect on hypothalamo-pituitary-gonadal axis is a rodent study as well (Yilmaz. 1999).
Figure 1: Mean (± SEM) plasma testosterone concentrations over a 6-h sampling period of control and melatonin-treated young rams (**, *, NS: per sampling time, differences between treatments groups are highly significant (P < 0.01), significant(P < 0.05) or non-significant respectively | Rekik. 2015).
Now in contrast to the Rekik study from last week where the rodents received melatonin releasing implants, Yilmaz et al. injected the rodents with a whopping dose of 0.5mg/kg melatonin per day (no information on when they did it, but if they did it when the rodents were supposed to be awake, this alone could explain all sorts of negative effects | see "When Timing Matters - Melatonin").

While both are different from the regular procedure in humans who would obviously take a single melatonin pill (no injections or implants) before bed, the low dose melatonin the implants in the Rekik study delivered into the blood stream is probably a better proxy for the effects of the low dose of melatonin that will actually make it into the circulation from oral supplements.
While supplementation clearly doesn't mess w/ T-levels, there is data that indicates that male patients with GnRH deficiency have increased nocturnal melatonin secretion while in hypergonadotrophic hypogonadal males melatonin secretion is decreased. It is thus obvious that the two hormones are - as all of the important endocrine hormones - linked in one way or another (Luboshitzky. 1997). Therfore it is not surprising that testosterone treatment normalized melatonin concentrations in hypogonodal men, which provides additional evidence that the two can hardly be antagonists.
"If", "likely" and "proxy" are yet not the words I like to use when I am trying to present conclusive evidence. That's why I am happy that researchers from the Haemek Medical Center did a study that can be considered "evidence" without "ifs" and "proxies". In their study, Luboshitzky et al. (2000) studied the effects of melatonin of 6 mg given orally every day at 1700 h for 1 month in a double-blind, placebo controlled fashion, on the nocturnal secretory profiles of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and inhibin β in six healthy adult men. The serum concentrations of LH, FSH, testosterone and inhibin β were determined before and after treatment every 15 min from 1900 to 0700 h over 3 nights in a controlled dark-light environment with simultaneous polysomnographic sleep recordings.
Figure 2: Luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone levels expressed relative to baseline. There are no significant differences in response to 6 mg of melatonin per day (Luboshitzky. 2000)
What the found were no statistically significant differences in either LH, FSH, testosterone and inhibin β integrated nocturnal secretion values during the whole treatment period. Likewise, their pulsatile characteristics during melatonin treatment were not different from baseline values. As the scientists poin tout: "Taken together, these data suggest that long-term melatonin administration does not alter the secretory patterns of reproductive hormones in normal men" (Luboshitzky. 2000).
There is a way in which melatonin can mess with your health. If you take it anywhere but 1-2h before bed (with the exception of anti-jet lag treatment) it can mess with your metabolic and hormonal health | learn more.
No, no and no! Since Luboshitzky's study from 2000 is not the only study that showed no effect of melatonin on testosterone (Weinerg. 1980; Wright. 1986, Petterborg. 1991), I can only repeat what I told those of you who message me before: There is no conclusive evidence that melatonin administered correctly, i.e. before bed, would have negative effects on the amount of testosterone that's floating through your veins.

I hope this settles your concerns, because meltatonin is, as I have pointed out in several previous articles quite a marvelous supplement. Not a "must have", but certainly one of the supplements that ranks very high on the "certainly useful" scale | Comment on Facebook!
  • Luboshitzky, Rafael, et al. "Abnormal melatonin secretion in hypogonadal men: the effect of testosterone treatment." Clinical endocrinology 47.4 (1997): 463-469.
  • Luboshitzky, Rafael, et al. "Long-term melatonin administration does not alter pituitary-gonadal hormone secretion in normal men." Human reproduction 15.1 (2000): 60-65.
  • Petterborg, L. J., et al. "Effect of melatonin replacement on serum hormone rhythms in a patient lacking endogenous melatonin." Brain research bulletin 27.2 (1991): 181-185.
  • Rekik, Mourad, et al. "Melatonin administration enhances the reproductive capacity of young rams under a southern Mediterranean environment." Animal Science Journal (2015).
  • Weinberg, Uzi, et al. "Melatonin Does Not Suppress the Pituitary Luteinizing Hormone Response to Luteinizing Hormone-Releasing Hormone in Men*." The Journal of Clinical Endocrinology & Metabolism 51.1 (1980): 161-162.
  • Wright, J., et al. "The effects of exogenous melatonin on endocrine function in man." Clinical endocrinology 24.4 (1986): 375-382.
  • Yilmaz, Bayram, et al. "Melatonin inhibits testosterone secretion by acting at hypothalamo-pituitary-gonadal axis in the rat." Neuro endocrinology letters 21.4 (1999): 301-306.
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