In the U.S. and many other countries, prescription drugs are medications that require a prescription to be dispensed. These medications are typically stronger than over-the-counter drugs, and can only be used by the intended person to treat a specific medical diagnosis. Prescription drugs are only distributed at licensed pharmacies.

Over-the-counter drugs are medications people can purchase without a prescription at drug stores, grocery stores, or other stores. OTC medicines treat a variety of illnesses and their symptoms, including pain, coughs and colds, diarrhea, constipation, acne, and others. There are quite a few prescription drugs that are available as OTC drugs because, when sold over-the-counter, the dosage is much lower than it is in the medication's prescription form.

Different countries have differing definitions of what’s a prescription drug and what’s not, which means that some drugs available only with a prescription in the U.S. may be obtainable without one elsewhere. And vice versa.