This Technical Assistance Publication (TAP), Clinical Drug Testing in Primary Care, is for clinical practitioners- physicians, nurse practitioners, and physician assistants- in health centers. The publication provides information that practitioners need when deciding whether to introduce drug testing in their practices and gives guidance on implementing drug testing. The TAP does not address drug testing for law enforcement or legal purposes, nor does it include testing for the use of anabolic steroids or performance-enhancing substances. This TAP describes some of the ways that drug testing can contribute to the assessment, diagnosis, and treatment of patients seen in primary care, the management of the treatment of chronic pain and the identification and treatment of substance use disorders.