Opioids are underused by physicians for the treatment of cancer pain. Reasons for this include excessive concern about opioid-induced respiratory depression, tolerance, and addiction, as well as the impact of controlled substances regulations. The negative impact of controlled substances regulations on patient care is not well understood. This paper reviews the historical basis and current structure of the regulatory system. Four potential ways in which controlled substances regulations and policies can affect medical care are discussed: (1) by placing restrictions on physician practice, (2) by affecting patient access to opioids, (3) by stigmatizing patients, and (4) indirectly through physicians' perceptions of regulations, resulting in modified medical practices. Physicians are urged to work with state regulatory agencies to identify regulatory impediments to appropriate patient care.