Drug abuse has significant cost to the individual, the family and the society. This study aimed to assess out of-pocket costs of consequences of drug use disorder. Data were drawn from the Iranian Mental Health Survey (IranMHS) through face-to-face interviews with 7841 respondents aged 15–64 years. We used a bottom-up cost-of-illness method for economic analysis. Out-of-pocket costs for treatment of mental and drug problems, treatment of medical illnesses, as well as costs of crimes were assessed. The average of total annual expense was US$ 2120.6 for those with drug use disorder, which was 23.5% of annual income of an average Iranian family in the year 2011. The average of total out-of-pocket cost was US$ 674.6 for those with other mental disorder and US$ 421.9 for those with no mental disorder. Catastrophic payment was reported in 47.6% of the patients with drug use disorder and 14.4% of those with other mental disorder. Thus, considerable amount of family resources are spent on the consequences of drug use.