What is maximum safe dosage of melatonin for teens?

There's been no evidence that melatonin is a drug that is capable of an OD. Personally, I've taken several mgs (upwards of 20) and was fine. The only drawback is that you'll feel very groggy in the morning. Also, don't use too much, well, too much. Melatonin is a naturally occurring drug that is excreted from the pineal gland in the absence of light. If you continue to regularly take melatonin every night, it can temporarily disrupt melatonin production in the brain. It's not life-threatening by any means, but it can severely disrupt your natural sleep schedule.