Over-the-counter (OTC) drugs are medicines that may be sold to a customer without a prescription from a health care professional, as compared to prescription drugs, which may only be sold to customers possessing a valid prescription. In many countries, OTC drugs are selected by a regulatory agency to ensure that they are products that are safe and effective when used without a physician's care.

The term over-the-counter may be somewhat counter-intuitive, since, in many countries, these drugs are often located on the shelves of stores like any other packaged product. In contrast, prescription drugs are almost always literally passed over a counter from the pharmacist to the customer. Some drugs may be legally classified as over-the-counter (i.e. no prescription is required), but may only be dispensed by a pharmacy employee after an assessment of the patient's needs and/or the provision of patient education. In many countries, a number of OTC drugs are available in establishments without a pharmacy, such as general stores, supermarkets, gas stations, etc. Regulations detailing the establishments where drugs may be sold, who is authorized to dispense them, and whether a prescription is required vary considerably from country to country.