Opioids are the major class of analgesics used to relieve moderate to severe pain in patients with advanced illness such as incurable cancer or other end-stage diseases, including end-stage cardiovascular disease or chronic obstructive pulmonary disease (COPD).2,5,8
Opioids bind to mu–opioid receptors in the central nervous system (CNS), providing analgesia, but they also bind to peripheral mu–opioid receptors in the gastrointestinal tract, inhibiting bowel function.2
Effects of opioids on the gastrointestinal tract include:
Small intestine2
- Decreased propulsive contractions
- Increased water absorption
Large intestine2
- Decreased propulsive peristalsis
- Increased nonpropulsive contractions
- Increased anal sphincter tone
- Decreased reflex relaxation response
- Increased transit time
- Increased desiccation of feces
