Diphenhydramine is a anti-histamine and nausea control medication I believe, has recreational value but not one I am willing to take. Acetaminophen is like asprin, it won't get you high and it has toxic metabolites. Doxylamine succinate is also an anti-histamine found in OTC medications, slightly less powerful then diphenhydramine, its also been used as a sleep aid. Dextromethorphan is an OTC opioid analgesic, has a higher recreational value but still only for the desperate, or very adventurous.
Just google dxm, or dextromethorphan. Check erowid.org, read reports and use their resources.