| S.No. | Organ system | Adverse effects |
| 1 | Respiratory system | Respiratory depression, obstructive and central sleep apnea, ataxic breathing, respiratory arrest, and death | 2 | Central nervous system | Increased risk of falls, cognitive impairment, myoclonus, delirium, depression, somnolence, and sleep disorders | 3 | Cardiovascular system | Orthostatic hypotension, bradycardia, vasodilation, and an increased risk of cardiovascular events, e.g., myocardial infarction | 4 | Gastrointestinal system | Constipation, nausea and vomiting, gastric reflux, delayed gastric emptying, abdominal cramping, and distension | 5 | Immune system | Decreased wound healing, pruritus, altered cytokine production, increased histamine release, inhibition of macrophage, neutrophil, and natural killer cell activity and recruitment, increased HIV replication, and cancer progression | 6 | Endocrine system | Opioid-induced endocrinopathy (usually only with high opioid doses, long-term), resulting in decreased libido, testicular atrophy, early menopause, and sexual dysfunction |
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