| Source | Serum half-life (hours)* | Approximate equivalence to 10 mg morphine injection (mg) | Important clinical features |
| IMPORTANT: The doses included here are NOT recommended for the initiation of therapy; they provide equivalents for the purpose of comparing different opioids. | |||
| Natural | |||
| Morphine | 1.9 +/– 0.5 | 10 SC/IM/IV 30 PO | |
| Codeine | 2.9 +/– 0.7 | 75 SC/IM/IV 130 to 200 PO | Metabolized by CYP2D6 to active drug (morphine). Metabolism and effects are subject to pronounced individual variability. Single oral doses over 65 mg tend to produce disproportionately greater adverse effects than analgesia. |
| Semi-synthetic | |||
| Hydromorphone | 2.4 +/– 0.6 | 1.5 SC/IM/IV 7.5 PO | Hepatically metabolized to metabolites that can accumulate in organ failure and prolong effects. Some metabolites have been linked to neurotoxicity. |
| Oxycodone | 2.6 (2.1-3.1) | 20 to 30 PO | Metabolized by CYP3A4 and 2D6. Prolonged effects and elevated serum concentrations with renal or hepatic insufficiency. May cause QTc prolongation. |
| Hydrocodone | 4.24 +/– 0.99 | 30 PO | |
| Diacetylmorphine (diamorphine, heroin) | 5 SC | Highly lipophilic causing more rapid CNS effects than morphine. Largely metabolized to morphine. Due to abuse potential is not available for clinical use in many countries. | |
| Synthetic | |||
| Meperidine | 3.2 +/– 0.8 | 75 to 100 SC/IM 300 PO | Excitatory neurotoxicity may occur when normeperidine, a renally-eliminated metabolite, accumulates. |
| Methadone | 27 +/– 12 | 10 SC/IM/IV Highly variable. See clinical features. | Used in opioid substitution therapy. Can cause QTc prolongation. May be far more potent than indicated in this table. Metabolized by CYP3A4. Due to its highly variable and prolonged half-life (up to 150 hours), methadone has the highest risk among opioids of accumulation and toxicity during initial titration and after changes in dose. |
| Tramadol | 5.5 (4.5-7.5) | 50 to 100 PO¶ | Usual initial dose for mild analgesia shown; NOT equivalent to parenteral morphine 10 mg. Effects NOT completely reversed by naloxone. Noted to cause seizures. Metabolized by CYP2D6 and 3A4. Subject to interactions including serotonin excess. |
| Fentanyl | 3.7 +/– 0.4 | 0.05 to 0.1 SC/IM/IV | Short acting when administered IV/IM as a single dose. Highly lipophilic. Parent drug accumulates with repeated or prolonged administration. |
| Agonist/antagonist | |||
| Pentazocine | 2 to 3 | 30 to 60 SC/IM 75 to 150 PO | |
| Partial agonist | |||
| Buprenorphine | 2.33 +/– 0.24 | 0.3 to 0.4 IM/IV 0.4 SL | Used in opioid substitution therapy. Significantly longer duration of effect than 10 mg parenteral morphine. Metabolized by and subject to interactions involving CYP3A4. |
| Gastrointestinally insoluble - not analgesic | |||
| Diphenoxylate | 2.5 to 5 PO (anti-diarrheal dose)¶ | Poor solubility limits potential for parenteral injection and abuse. Usually formulated with atropine (United States trade name Lomotil, 0.025 mg atropine and 2.5 mg diphenoxylate) to further decrease abuse potential. | |
| Loperamide | 2 to 4 PO (anti-diarrheal dose)¶ | CNS depression and cardiac conduction disturbances are observed in large acute and chronic supratherapeutic ingestions. | |
