Lack of patient compliance with prescribed pharmaceuticals is a huge drain on health-care systems. The most widely cited estimate is that it costs the U.S. system over $100 billion annually, accounts for 100,000 deaths, and 1,000,000 hospitalizations.

Poor patient compliance has been documented in nearly every field of clinical medicine. It affects chronic (eg: diabetes mellitus, hypertension, schizophrenia, HIV) and acute therapy situations (eg: antibiotic treatment of infections).

Patient non-compliance has enormous implications for clinical trials. There are several areas of clinical research where noncompliance has significant negative consequences. Drugs may be erroneously determined to be ineffective and abandoned, at huge cost to the developing company. Non-compliance also affects the signal-to-noise ratio (see below) in clinical trials research, causing the approval process to be drawn out, again at considerable cost to the developer.