Serotonin Syndrome: Circumstances of serotonin syndrome, a potentially life-threatening situation, have been described throughout concomitant utilization of opioids with serotonergic drugs. Marked differences might exist during the analgesic effect provided by codeine as a result of genetic variations within the CYP 2D6 liver enzyme accountable for metabolizing codeine into morphine. https://codeine.store/codeine-phosphate-15-mg-ulotka/