Many new drugs have fewer side effects than old ones. This development is an outgrowth of scientific advances in genetics and chemistry that allow drugmakers to more precisely target a drug's action in the body. Those developments have created a topsy-turvy world in which many of the safest drugs require a doctor's prescription, while older drugs with potentially dangerous side effects can be bought at any grocery store. But the non-prescription drug industry worries that forcing drugs over the counter against the desire of manufacturers is not in the public's best interest and could discourage investment in new drugs. If you think about it, the manufacturer has the safety data, the treatment profiles, all the information to know when a switch makes sense.
Nobody knows the molecule better than the manufacturer.
How drugs go OTC Federal law requires that all drugs safe enough to be sold without a prescription be made available over the counter. But, in practice, the FDA lets drug companies determine when a drug moves over the counter. As the patent expiration nears, drug companies ask the FDA to switch the drug over the counter. If the switch is approved, the company can get three more years of competition-free exclusivity. Swedish drug company AstraZeneca is following this strategy with Prilosec.