The amount of melatonin in the same supplement brand can vary wildly from one batch to the next, sometimes by over 400%. This means you can't really trust that you're getting the same dose every time you buy it, even if it's the exact same bottle.

The amount of melatonin in store-bought sleep aids often doesn't match what's printed on the label. In fact, many pills contain way more or way less than advertised, making it hard to know exactly what dose you're actually getting.

In the U.S., you can buy melatonin pills without a prescription, but they’re not checked like real medicines—so some pills might have way more or less melatonin than the label says, or even contain weird stuff you didn’t sign up for.

Many over-the-counter melatonin pills don't actually contain the amount of melatonin listed on the bottle. In fact, some have way more, some have way less, and a few don't have any melatonin at all.

A small test of 10 melatonin pills bought in the U.S. found that 4 of them had way more or way less melatonin than what was printed on the bottle — so you might not be getting what you think you're paying for.

Some melatonin pills you can buy in the U.S. have strange, unknown chemicals in them—up to 1% of the pill—which isn't supposed to be there, even though they pass safety checks for the stuff they're supposed to contain.