Drug addiction, also called substance dependence or chemical dependency, is a disease that is characterized by a destructive pattern of drug abuse that leads to significant problems involving tolerance to or withdrawal from the substance, as well as other problems that use of the substance can cause for the sufferer, either socially or in terms of their work or school performance.
The term dual diagnosis refers to the presence of both a drug-abuse or dependence issue in addition to a serious mental-health problem in an individual. Substance abuse or dependence unfortunately occurs quite commonly in people who also have severe mental illness. Individuals with dual diagnosis are also at higher risk of being noncompliant with treatment.
Drugs most often associated with this term include: alcohol, substituted amphetamines, barbiturates, benzodiazepines (particularly alprazolam, lorazepam, diazepam and clonazepam), cocaine, methaqualone, cannabis and opioids.