North American brand of a painkiller whose active ingredient is acetaminophen (AKA paracetamol outside North America).
Don't take more than the recommended dose of this stuff (or of any other paracetamol/acetaminophen based painkillers). Overdose can cause liver failure, a fairly unpleasant way to die.
There are tales of people overdosing on tylenol/paracetamol pills one evening, and waking up the next morning feeling sheepish... they go about their business as normal, then later that afternoon start to feel really ill, get rushed to hospital and die shortly afterwards because their liver is knackered.
Taking a handful of Tylenol PM and then trying to have an orgasm before you fall asleep. Something that has been rumored as impossible by old people everywhere.