Substance abuse, also known as drug abuse, is the use of a drug in amounts or by methods which are harmful to the individual or others. It is a form of substance-related disorder. Substance use disorders (SUD) are mental health conditions that arise from chronic drug use. There is an increased recognition of this problem in Saudi Arabia. Drugs of abuse testing is the detection of one or more illegal and/or prescribed substances in the urine, blood, saliva, hair, or sweat. Testing detects substances not normally found in the body. Drug abuse testing usually involves an initial screening test followed by a second test that identifies and/or confirms the presence of a drug or drugs. Initial screening is done by urine tests and confirmation is done by blood tests. Major drug class screened are Amphetamines, Barbiturates, Benzodiazapines, Cannibinoids, Cocaine, methadone and opiates. In this article we reviewed lab diagnosis of drug of abuse.