In a market glutted with over-the-counter sleep aids, melatonin is one of the most popular. A naturally occurring hormone, it governs the sleep-wake cycle and is sold as a dietary supplement to help battle insomnia, jet lag and other conditions. Melatonin sales are rising fast in the U.S., from $285 million in 2016 to $820 million in 2020, according to the market research group Statista.

But melatonin’s ubiquity poses dangers for kids, finds a new study published by the U.S.