• Nausea and vomiting: females are at increased risk; in high-risk patients, prevention strategy includes propofol, epidural analgesia, and multimodal therapy that may include an dopamine antagonist and a steroid
• Gastrointestinal effects: delayed gastric emptying, sphincter of Oddi spasm, acute urinary retention; treat with naloxone or peripherally acting methynaltrexone
• Skeletal muscle effects: potent, high-dose opioids, especially when given rapidly, cause skeletal muscle rigidity, which includes the thoracic, abdominal, and pharyngeal muscles; may impair ventilation and require intervention with a muscle relaxant
• Histamine release: morphine, codeine, and meperidine but not fentanyl
• Pruritus: typically of the nose; common after spinal opioids injections
• Pupil effects: miosis
• Diffuse CNS effects: dizziness, sedation, drowsiness, euphoria, dysphoria, cognitive dysfunction
• Cardiovascular effects: activation of vagal nuclei, direct myocardial depression, venous dilation

CNS = central nervous system.