BACKGROUND Withdrawal syndrome may influence patient's motivation for participation in addiction treatment programs. Management of the symptoms can improve the success rate of addiction treatment programs. In the present study, we have evaluated the efficiency of an herbal product as adjunct therapy for alleviation of withdrawal syndrome in opium abuse. METHODS In the present clinical trial, 81 patients were assigned into case and control groups. The control group was treated with methadone and placebo for 4 weeks. The case group was treated with methadone and powdered dried leaves of Rosmarinus officinalis for the same interval. Occurrence of withdrawal syndrome was compared between groups on days 3, 7, and 14 after beginning of the treatment, and the possible signs and symptoms of withdrawal syndrome were checked. The clinical opioid withdrawal scale (COWS) was used for evaluation of withdrawal syndrome in the patients. FINDINGS Patients in the case group experienced less severe withdrawal syndrome compared to those in the control group; chiefly bone pain, perspiration, and insomnia. CONCLUSION The present study showed that rosemary can be used as an optional extra drug for treatment of withdrawal syndrome during treatment programs for opium addiction and possibly addiction to other opioids.