Melatonin is safe to take daily

Dear Dr. Roach: In a recent column, you responded to a reader asking about the link between Benadryl and dementia, and near the end you mentioned that melatonin is “very safe.” I’ve heard that taking melatonin can affect your body’s natural production of melatonin, causing a loop — the more you take, the less your body will produce — thus necessitating a person to continue taking it indefinitely. Would you speak to this? — L.P.

Answer: Many hormones do have what is called a feedback loop, where high blood levels of the hormone will prevent the body from making more. That is the case, for example, with thyroid hormone. High levels of thyroid hormone, whether made by the body or taken as a medication, will shut off production of more thyroid hormone, preventing excess. However, if you stop taking thyroid hormone, the body will sense this and restart production of thyroid hormone. In some cases, it takes a period of time to restart synthesis, during which the body has low hormone levels.

This does not appear to be a major issue with melatonin, which has a very short lifetime inside the body, and whose secretion is largely regulated by the length of daylight. As such, it is less likely than other treatments to cause a “rebound” — a worsening of insomnia after stopping it. However, the situation is complex, and some people certainly might notice such an effect. It is also true that melatonin levels tend to decrease with age.

Melatonin, at low dose — such as 0.5 to 1 mg — is indeed thought to be very safe. There are no perfectly safe substances: Anything can be dangerous at the right dose. Headache, confusion and fractured sleep have been reported in people taking melatonin at doses up to 36 mg.