Drugs are notoriously difficult to define and yet present some of the most difficult ethical issues for the science and technology on which they are based. At the simplest level, drugs are molecules whose biochemical effects have been classified as socially desirable or undesirable in different times and places. Dorland's Medical Dictionary defines a drug as a "chemical compound that may be used on or administered to humans or animals as an aid in the diagnosis, treatment, or prevention of disease or other abnormal condition, for relief of pain or suffering, or to control or improve any physiologic or pathologic condition" (p. 510). But this ignores so-called recreational drugs, which may be described as substances used mainly for their psychoactive properties and pleasurable effects.

Historically drugs have been derived from plants and other natural materials and thus their production relied on indigeneous forms of knowledge and premodern techniques, often...