Introduction- Opium is one of the most common substance abuse in Asian countries.In this cross sectional study we clarify the effects of opium on respiratorysystem and possible mechanism of respiratory involvement ,Method: The casecontrol study was done on two groups of men between the ages of 30-50 years. Thecase group was of 100 opium addicts. Thecontrol Group was of 100 healthy nonopium addicts. All of the 200 men underwent spirometryand the results comparedwith each other. Result: In the opium addicts the mean FVC was 3.10± 0.62L whichis significantly lower than normal value (4.2L in males).In controls, the mean FVCwas 3.60±0.54L.P value for FVC was <0.001 which shows a significant