, opioid , or opioid analogs such as loperamide , codeine , diphenoxylate ) in diarrhea-predominant IBS for mild symptoms and stronger opiates such as morphine and oxycodone for severe cases. [79] [80] [81] Drugs affecting serotonin (5-HT) in the intestines can help reduce symptoms. [82] Serotonin stimulates the gut motility