Melatonin is a hormone that our bodies make naturally in small amounts (about 0.3 milligrams) to set our sleep-wake cycles. When melatonin is released by our brain’s pineal gland and a few other organs, we start to feel drowsy. But if you regularly take exogenous (aka supplemental) melatonin, it’s unclear how that will affect the rest of your hormones. There’s some research to show that melatonin supplements can negatively affect the function of hormones like estrogen and male growth hormone, for example.
And while taking melatonin for a quick reset (if you’re traveling across multiple time zones, for example) can help you adjust to a new bedtime, there’s little credible evidence that it will improve your overall sleep quality. Instead, it can leave you feeling groggy, foggy, and dazed the day after a subpar rest—another reason it’s not as widely available in other countries.
“The main concern for me,” Byrnes adds, “Is that you can develop a tolerance to it, so over time you need a higher and higher dose. In the long run, you’re just making it so much harder to fall asleep naturally.”
When Byrnes arrived in the States to work as a nutrition researcher at mbg, she was surprised to find not only melatonin online and on the shelves of stores she visited—but very high doses of it. Some melatonin supplements contain 10 milligrams of the hormone or more—that’s 33 times higher than the amount your body produces naturally. “It blew my mind a bit, to be honest,” she says. “The contrast was so stark.”