Melatonin
MT1 · MT2

Melatonin is the messenger that tells the body night has fallen and, above all, what time it is. It is a hormone produced by the pineal gland when the retina detects darkness, and from there it acts as a clock that tells the rest of the body when nighttime functions are due and when daytime ones are.

Melatonin is not a sleeping pill. What it does is more like setting the time than anesthetizing sleep, and that is why it works better if the problem is when you feel sleepy.

Its most solid evidence is in timing problems: jet lag when crossing several time zones eastward, delayed phase disorder (falling asleep in the small hours even when you want to sleep earlier), and the misalignment of shift workers. In common insomnia the effect exists, but is small: it trims 4 to 7 minutes off how long you take to fall asleep.

It makes the most sense for you if you fly frequently across time zones, work rotating shifts, or struggle to fall asleep before 2 or 3 in the morning no matter how hard you try. Outside those timing patterns, the benefit you can expect is more modest.

Important: the use in children, including for insomnia within autism (where there is solid clinical evidence), must always be prescribed and supervised by a healthcare professional, never a decision parents make on their own.

Less is usually more. A small dose, similar to what your body produces naturally, performs as well as or better than one ten times larger, and without the side effect that does appear with the high dose: melatonin keeps circulating in the blood well into the morning and can leave residual drowsiness.

Timing matters more than the amount. To advance the clock (eastward jet lag, a delayed internal clock), the studied time is the afternoon, several hours before the desired bedtime. To delay the clock (westward jet lag), it is shortly after waking, not at night.

A significant part of the melatonin you take by mouth is lost before it reaches the blood: the liver processes and removes a good portion of it on its first pass. That is the reason the usual oral doses (1 mg or more) are higher than the amount your body produces naturally in a night.

No, and here melatonin has a serious problem: what the label says and what is inside the bottle do not always match, and sometimes there is a lot of difference. An analysis of commercial products (Erland and Saxena, 2017) found actual contents ranging from 83% below the stated amount to 478% above, with more than 7 out of 10 products outside a reasonable margin (±10%) relative to their label.

USP Verified or NSF check that the actual content matches what is declared (seals uncommon in Europe). In the sports context, where avoiding banned substances also matters, examples of that kind of seal are Informed Sport or NSF Certified for Sport.

In the short term, in healthy adults, melatonin has a good safety profile. Even so, there are situations in which it is wise to talk to a doctor before taking it and one, above all, in which the decision should never be made at home without supervision:

• Children and adolescents. However many over-the-counter products with a harmless appearance exist, melatonin in minors is not self-care. Its pediatric use, including in the autism context where there is solid clinical evidence, must always be prescribed and supervised by a healthcare professional.
• Pregnancy and breastfeeding. It is not recommended, due to a lack of sufficient clinical data —not because firm proof of risk exists, but because the evidence needed to rule it out with confidence is not there.
• Treatment with fluvoxamine (an antidepressant). This combination is documented and is one of the most relevant interactions in this whole guide: fluvoxamine can multiply melatonin blood levels by 17. While on fluvoxamine, medical assessment before adding melatonin is necessary.
• Driving and operating machinery. The effect can persist for several hours; the usual caution period is the 4-5 hours after taking it.

As with any supplement, the above is information, not a substitute for a doctor’s assessment, especially with other ongoing medication or a diagnosed chronic illness.