An ad for curing tobacco addiction, a form of drug addiction.

A drug addict, in New york; photo from 2014.

Drug addiction, also called substance dependence or dependence syndrome, is a condition where a person feels a strong need to take a drug. Addiction also involves other behaviours. These include finding it difficult to control the need to use the drug and feeling the use of the drug to be more important than more normal things such as family or work. When the person does not use the drug for an amount of time, they may suffer from withdrawal.