Abstract: The invention provides for compositions and methods of reducing pain in a subject by administering a combination of mu-opioid receptor agonist, kappa1-opioid receptor agonist and a nonselective opioid receptor antagonist in amounts effective to reduce pain and ameliorate an adverse side effect of treatment combining opioid-receptor agonists. The invention also provides for methods of enhancing an analgesic effect of treatment with an opioid-receptor agonist in a subject suffering from pain while reducing an adverse side effect of the treatment. The invention also provides for methods of reducing the hyperalgesic effect of treatment with an opioid-receptor agonist in a subject suffering from pain while reducing an adverse side effect of the treatment. The invention further provides for methods of promoting the additive analgesia of pain treatment with an opioid-receptor agonist in a subject in need while reducing an adverse side effect of the treatment.