You can take approximately 150mg, 30 minutes before sleep. 4) Melatonin Pills: 1.5mg daily taken 30-60minutes before bed. Melatonin occurs naturally in our body and helps to regulate the body’s circadian rhythm, our internal 24-hour time keeping system, that can affect our sleeping cycles Three mg of melatonin is a lot. Either you are a very large sixteen year old or your doctor or pharmacist may have made a mistake.