I have obstructive sleep apnea so I have difficulty sleeping and staying asleep (I am aroused [from sleep, I am not using the word with sexual connotations )anyway melatonin is a growth releasing hormone or something like that, and 2 mg will put you to sleep and keep you there for over 5 hours. You can buy more mgs but try 1mg or 2mg first. It is safe and nonaddictive. Tylenol PM uses an antihistamine to make one sleepy, and others have covered that pretty well; but, remember that it is the tylenol that is responsible for how many pain meds (like hydros with tylenol) a doctor can prescribe. We can take 240mg of hydrocodone per day but only 4 grams is the limit for Tylenol. Some deaths, according to McNeil, have occurred with 4 g of tylenol. That is the exception I think, but when we get close to 10grams of Tylenol we are getting ourselves into health problems. N-acetyl Cystine can help reverse the damage tylenol does and I think Milk Thissle helps too. With all of the OTC products we take as well as pain meds that require a prescription, taking Tylenol PM for sleep is a bit risky. Just be careful