Stole this from Wiki for you --
As a general rule, (in the USA) over the counter (OTC) are used to treat a condition that does not need care from a healthcare professional if have been proven to meet higher safety standards for self-medication by patients. Often, a lower strength of a drug will be approved for OTC use, but higher strengths require a prescription to be obtained; a notable case is ibuprofen, which has been widely available as an OTC pain killer since the mid-1980s, but it is available by prescription in doses up to four times the OTC dose for severe pain that is not adequately controlled by the OTC strength.
Herbal preparations, amino acids, vitamins, minerals, and other food supplements are regulated by the FDA as dietary supplements. Because specific health claims cannot be made, the consumer must make informed decisions when purchasing such products.
Physicians may legally prescribe drugs for uses other than those specified in the FDA approval, known as off-label uses. Drug companies, however, are prohibited from marketing their drugs for off-label uses.
Large US retailers that operate pharmacies and pharmacy chains use inexpensive generic drugs as a way to attract customers into stores. Several chains, including Walmart, Kroger, Target, and others, offer $4 monthly prescriptions on select generic drugs as a customer draw. Publix Supermarkets, which has pharmacies in many of their stores, offers free prescriptions on a few older but still effective medications to their customers. The maximum supply is for 30 days.