[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) › Morphine [Pharmacology](https://durgical.com/en/pharmacology/) · [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) # Morphine The reference opioid for severe pain and cancer pain. It activates the μ receptor; it can depress breathing and causes constipation. Updated 2026-11-01 - Class: [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) - Receptor: μ-opioid receptor - ATC code: N02AA01 - WHO Model List of Essential Medicines ◎**μ-opioid receptor**Morphine ⓘ The figure shows morphine in the μ receptor bound to its Gi protein; the viewer crops the image to the receptor. **Target in 3D:** μ-opioid receptor. PDB structure 8EF6 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/8EF6) · Drag to rotate · pinch to zoom ## Mechanism of action Morphine, a natural opium alkaloid, is a full agonist at the μ receptor. It activates the Gi protein, which closes presynaptic calcium channels and opens potassium channels, reducing pain transmission in the spinal cord and brainstem; it also changes the emotional experience of pain. The same receptors in the brainstem and gut explain respiratory depression, miosis and constipation. - Binds and activates the μ receptor on pain-pathway neurons - The Gi protein closes Ca²⁺ channels and opens K⁺ channels - Less glutamate and substance P are released in the dorsal horn - Relief of severe pain; in the brainstem, less drive to breathe ## Pharmacokinetics **Absorption** Less drug reaches the blood by mouth because of hepatic first-pass metabolism. **Metabolism** Liver, mainly by glucuronidation (UGT2B7): morphine-3-glucuronide, inactive, and morphine-6-glucuronide, active. **Elimination** Kidney, mainly as glucuronides, which build up in kidney disease. **Half-life** Between 1.5 and 4.5 hours, depending on the study. **Onset and duration** Intravenously, the peak effect on the nervous system takes about 30 minutes. ## Indications - Pain of acute myocardial infarction [Myocardial Infarction (Heart Attack) →](https://durgical.com/en/conditions/myocardial-infarction/) - Cancer pain, such as that of advanced lung cancer [Lung cancer →](https://durgical.com/en/conditions/lung-cancer/) - Severe acute postoperative or trauma pain - Breathlessness in palliative care ## Adverse effects ### Common - Constipation - Nausea and vomiting - Drowsiness - Itching from histamine release - Urinary retention - Miosis ### Serious (rare, important) - Respiratory depression - Hypotension - Dependence, opioid use disorder and withdrawal - Stronger, longer opioid effect from build-up of the active glucuronide in kidney disease ## Contraindications - Significant respiratory depression without monitoring or support - Severe acute asthma - Paralytic ileus or bowel obstruction - Use of monoamine oxidase inhibitors within the last two weeks ## Key interactions **Benzodiazepines, alcohol and other CNS depressants** Add sedation and respiratory depression, with risk of death. **Monoamine oxidase inhibitors** Severe reactions, with high or low blood pressure and CNS depression. **Naloxone** Reverses its effects and can precipitate withdrawal in dependent patients. ## What is monitored - Respiratory rate and sedation level - Bowel habit - Kidney function ## Memory aid Morphine has two children: number 6, who keeps easing pain, and number 3, who does nothing. Both leave through the kidney; if the kidney fails, number 6 stays home and the effect drags on. ## Test yourself Think of the answer, then tap the question to see it. ## Why can morphine cause excessive, prolonged sedation in a patient with chronic kidney disease? Its active metabolite, morphine-6-glucuronide, is cleared by the kidney and builds up when kidney function falls, intensifying and prolonging the opioid effect. ## What explains the itching, flushing and orthostatic hypotension morphine sometimes causes? Histamine release and peripheral vasodilation. ## Why does oral morphine need more drug than intravenous morphine for the same effect? Because much of the morphine absorbed from the gut is metabolized in the liver before it reaches the circulation (first-pass effect). [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/morphine/) ## Related drugs - [Fentanyl](https://durgical.com/en/pharmacology/fentanyl/) - [Naloxone](https://durgical.com/en/pharmacology/naloxone/) ## Related conditions - [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/) - [Lung cancer](https://durgical.com/en/conditions/lung-cancer/) [← Back to the class: Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Morphine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682133.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [MORPHINE SULFATE injection](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9362eca1-2bc9-4f72-8895-0b9179bfeb2b) (DailyMed (U.S. National Library of Medicine), 2026); [Morphine](https://pubchem.ncbi.nlm.nih.gov/compound/5288826#section=Metabolism-Metabolites) (PubChem (NCBI), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N02AA01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/morphine/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/morphine/