Could use expert help with why narcotic pain relievers cause constipation?

Slow Bowel Down: There are many possible mechanisms as to why opioids cause constipation. The most common theories include that opioids cause increased anal sphincter tone slowing/stopping defecation. Opioids cause reduced peristalsis in the small intestine and colon slowing bowel movement. They also increased electrolyte and water absorption thereby dehydrating fecal material.