In the current study individuals with a history of drug abuse (users of heroin, cocaine, or amphetamine) displayed a 13-100% increase in body weight (self-reported) and exhibited a trend toward insulin resistance. Therefore, we investigated the effects of long-term altitude hiking on insulin sensitivity in this special population. Nine males recovering from drug addiction (ex-addicts) (age 28.7 +/- 1.3 years) and 17 control subjects (age 29 +/- 1.1 years) voluntarily participated in a 25-day hiking activity (altitude 2200-3800 M). On the 25th day of hiking, oral glucose tolerance test (OGTT), insulin response, lean body mass, fat mass, and waist-to-hip ratio (WHR) were measured in all subjects. After the altitude expedition, insulin levels during the OGTT in ex-addicts were similar to controls, suggesting that insulin sensitivity in this special population was normalized by long-term altitude activity. Along with improvements in insulin sensitivity, a significant reduction in WHR, but small increase in lean body mass, was observed. Twenty-five days of altitude activity significantly reverses hyperinsulinemia in the ex-addicts and this improvement appears to be partially associated with the reduction in central fatness.