Addiction refers to the repeated use of psychoactive substances, to the extent that the user is periodically or chronically intoxicated, shows a compulsion to take the preferred substance, has great difficulty in voluntarily stopping or modifying substance use, and exhibits determination to obtain psychoactive substances by almost any means. The life of the addict may be dominated by substance use to the virtual exclusion of all other activities and responsibilities. Addictions affect performance at work, family and social relationships, and can have severe consequences to physical and psychological health. 

There are many different classes of drugs that can cause addiction: alcohol; benzodiazepines like diazepam, temazepam and alprazolam; opiates such as heroin, methadone, morphine; and stimulants like cocaine or amphetamines. Medical treatment of chemical dependence may involve detoxification and medication to help promote or maintain abstinence. Dependence on substances is associated with a withdrawal syndrome when substance use is interrupted. For some clients the substances they use will mean that withdrawal symptoms will be temporary and tolerable; for others, the first part of addictions treatment will involve medical detoxification, which will usually involve medications that substitute for the drug of dependence, and medications that alleviate other symptoms of withdrawal. Once the detoxification is completed, promotion of abstinence may include a combination of medication and/ or therapy delivered in residential programmes offering primary, secondary or tertiary care, or outpatient settings through fellowships such as Alcoholics or Narcotics Anonymous, or individual therapy that might involve Cognitive Behavioural Therapy (CBT), Eye Movement Desensitisation and Reprocessing (EMDR) or counselling.