：
Drugs are substances used to prevent, treat and diagnose diseases. Theoretically speaking, drugs refer to all chemicals that can affect the physiological functions of organs and the metabolic activities of cells, belonging to the category of drugs, including contraceptives.
According to the law, drugs are divided into two categories: prescription drugs and over-the-counter drugs (OTC). Prescription drugs refer to drugs that can only be used under medical supervision in consideration of medical safety and must be prescribed in writing by medical practitioners (such as doctors, dentists or veterinarians).
Over-the-counter drugs refer to those drugs that are quite safe without medical supervision and can be sold directly by pharmacies without prescription. In the United States, the Food and Drug Administration (FDA) is the official organization that decides which drugs need prescriptions and which drugs can be sold directly in pharmacies.
The FDA appreciates that after years of prescription management, the drugs sold in pharmacies have a good safety record. Ibuprofen (analgesic) was originally a prescription drug, but now it can also be bought in ordinary pharmacies. Every tablet, capsule and dose of medicine sold in general pharmacies actually contain less active ingredients than the corresponding prescription drugs.
In the United States, although it takes many years for a new drug to be invented and approved for marketing, the inventor or discoverer of the drug can own the patent of its chemical structure 17 years. And as long as the patent is valid, the drug is the private property of the inventor.
Ordinary drugs (non-monopoly drugs) are not protected by patents. After the drug patent expires, the drug can be labeled as generic by all FDA-recognized manufacturers or drug dealers, and the price is lower than that when it is used as a monopoly drug.
Drugs only affect the speed of biological functions, and cannot change existing natural biological processes or produce new functions. For example, drugs can accelerate or slow down the biochemical reaction that causes muscle contraction, regulate the retention and elimination of sodium, secrete glands (such as mucus, stomach acid or insulin), and transmit information to nerves. The intensity of drug action usually depends on the reaction of the target site.