Drugs are obtained from many sources. Many inorganic materials, such as metals, are chemotherapeutic; hormones, alkaloids, vaccines, and antibiotics come from living organisms; and other drugs are synthetic or semisynthetic. Synthetics are often more effective and less toxic than the naturally obtained substances and are easier to prepare in standardized units. The techniques of genetic engineering are being applied to the production of drugs, and genetically engineered livestock that incorporate human genes are being developed for the production of scarce human enzymes and other proteins (see pharming).

Standards for drugs and tests for their identity, quality, and purity are given in the U.S. pharmacopoeia, first published in 1820 and at first revised every 10 years, later every 5 years. The British publish a similar pharmacopoeia. The National Formulary published by the American Pharmaceutical Association gives the composition, description, method of preparation, and dosage for drugs; the Physician's Desk Reference is a privately published compilation of information supplied by drug companies about their drug products, published yearly. The scientific study of drugs, their actions and effects, is pharmacology.

Legislation to safeguard drug purchasers began in the United States with the Pure Food and Drugs Act of 1906; this was superseded by the more inclusive and more stringent federal Food, Drug, and Cosmetic Act of 1938. Such laws are enforced by the Food and Drug Administration. The 1962 Kefauver-Harris amendments to the Food, Drug, and Cosmetic Act increased the authority of the Food and Drug Administration to regulate testing and marketing of new drugs. There are two marketing classes of drugs: ethical drugs, for which prescriptions are needed, and proprietary drugs, which are sold over the counter without prescription. Many of the latter, such as mouthwashes, gargles, and cold preparations, are only slightly, if at all, effective in curing ailments.