A previous podcast discussed how jet-lag medication was used to treat young people for sleep problems. A dietary supplement containing melatonin was readily available in health shops throughout the United Kingdom until it was banned. In some cases, melatonin supplements may also contain serotonin. 

Be mindful that the human body can make melatonin from the enzymatic conversion of serotonin into melatonin. There have been reports of poisoning in children who needed hospital care, and several young children died from a melatonin overdose.