otc drugs would either not work or would be an extremely slow death, either way an extremely painful and horrifying experience.
if youre dead-set on otc drugs, only one i can recommend (out of harm reduction) is cough syrup with only dextromethorphan as the active ingredient. do not use anything that contains acetaminophen/paracetemol, guafenesin, or any other additional active ingredients, because any of them would be incredibly painful and miserable to OD on.
most likely, you will just throw up any otc medicine you try to take before it can be fully absorbed. if you dont throw up early, the closest you'll get to dying is going into a coma. you might not even get that far and could just end up with permanent organ and brain damage and trauma while still being conscious enough to suffer through all of the consequences.