More young people are using melatonin to get to sleep, according to the Miami Herald.

Ugando is part of a growing trend of parents dispensing melatonin to children, particularly adolescents who don’t start feeling sleeping until well past 11. Though there are no figures on its use by teens and young adults, the sale of the supplement has risen steadily in the past five years, according to the Nutrition Business Journal. In 2007, sales came in at $90 million; by 2012 it was estimated to have tripled, to about $260 million.

Melatonin, known as the “hormone of darkness,” is manufactured by the pineal gland, a pea-sized structure located just above the middle of the brain. During daytime, there is very little melatonin in the body. At night, however, the pineal begins producing the hormone. The blood level of melatonin stays elevated for about 12 hours.

Much of melatonin’s popularity as a sleep aid is attributable to the fact that it can be bought over the counter. In fact, it is the only hormone available without a prescription. And it’s precisely this easy access that worries physicians, who point out that many other countries do require a script.