Findings indicate that inmate drug abuse is a serious and complex problem. The survey found that more than 76 percent of the inmate population (30,524 inmates) reported using controlled substances prior to commitment. Marijuana was the most frequently abused substance, followed by cocaine and narcotics. Specifically, marijuana use was reported by more than 13,000 inmates; cocaine in the powder form by 11,291; 'crack,' the cocaine derivative, by 1,229; narcotics, primarily heroin, by 11,217 inmates; hallucinogens such as LSD-25 and PCP by 1,613 inmates. Tabular data.