Codeine is an opium derivative that is rather similar to morphine in actions, uses, contraindications, precautions and adverse reactions. When given in the same dosage as morphine, the respiratory depression is the same, but orally administered codeine is about 60% of the potency of the parenteral, or not by mouth, version unlike morphine, which is potent in both methods of delivery. It causes more histamine release than morphine which may result in low blood pressure, flushing and sometimes constriction of the bronchi of the lungs.