Just a few of the main contenders that can harm you:
Tylenol, aka acetaminophen, can cause liver failure. A lot of cold, headache preparations also contain it.
Advil, Motrin, aka ibuprofen, can cause liver failure, ulcers, which can be fatal.
Imodium, aka loperamide, can cause fatal arrhythmias (heart abnormalities).
Antihistamines like benadryl, claritin, xyrtec, etc. can cause arrhythmias, and can be fatal, particularly in children.
Aspirin, bleeding ulcers that can kill you.
And that "herbal" and "natural" stuff and vitamins, watch out. A lot of bad actors there and it is not regulated as drugs but is considered dietary supplements.