There are certain drugs on the marketplace that have serious side effects - pharmaceutical drugs (most people know about the black market drugs, and if they don't, please refer to my brief dissertation about education about rather than banning drugs).
The pharmaceuticals I'm talking about need to be discussed with the patient by the doctor so that the patient understands and can weight the risks.
If a patient doesn't know or understand that there could be risks, or that the patient isn't physiologically capable of taking said drug (without blood/urine... tests) then no, the drug (concerned) should not be allowed over the counter.