Melatonin is naturally produced, but the hormone is one of the murkiest supplements on the market, unsubstantiated by incomplete and developing research, reports Van Winkle’s.

Given the lack of apparent side effects, it may seem harmless to label melatonin as a dietary supplement. But the classification matters for consumers, because the FDA doesn’t require supplements to include warnings of overdose risks on their labels, as is mandatory for drugs and hormones.

Perhaps even riskier, the classification allows companies to sell melatonin in varying dosages.

In 2001, researchers at MIT concluded that the correct dosage for melatonin falls between .3 and 1 mg. Yet, walk down the pharmacy aisle and you’ll see stacks of sleep aids packing as 10 times that amount.