ghezel hesar prison is the largest state prison in iran. as of 2011 it was holding about 20,000 prisoners, of which 13,000 were held on drug-related charges - said to be four times its planned capacity. it is located in ghezel hesar, city of karaj, 20 km northwest of the iranian capital tehran (there are two other prisons around karaj: rajai shahr prison and the central prison at karaj).