Formulary
Morphine: Uses, Dosing, Side Effects and Indian Brand Names
Morphine is the prototype mu-opioid receptor agonist and the reference standard opioid analgesic. It is used for severe pain, MI, cancer pain, and acute pulmonary oedema but carries risks of respiratory depression, dependence, and constipation.
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Morphine: Uses, Dosing, Side Effects and Indian Brand Names
Morphine is the prototype mu-opioid receptor agonist and the reference standard opioid analgesic. It is used for severe pain, MI, cancer pain, and acute pulmonary oedema but carries risks of respiratory depression, dependence, and constipation.
NEET PG High-Yield: Morphine is the prototype opioid -- every opioid concept is tested against it. Key points: tolerance does NOT develop to constipation and miosis. Naloxone is the specific antagonist. Morphine-6-glucuronide accumulates in renal failure. Morphine is CONTRAINDICATED in head injury (raises ICP) -- a perennial NEET PG MCQ.
Clinical overview
Morphine is the prototypical opioid analgesic and the gold standard against which all other opioids are compared for potency. Derived from the opium poppy (Papaver somniferum), it has been used therapeutically for over two centuries. In Indian clinical practice, morphine is indispensable for managing severe acute pain (myocardial infarction, trauma, post-surgical), cancer pain (per WHO analgesic ladder step 3), and acute pulmonary oedema (reduces preload and relieves dyspnoea). Its pharmacological profile includes analgesia, euphoria, sedation, respiratory depression, cough suppression, miosis, and constipation. Morphine is metabolised hepatically to two important metabolites: morphine-6-glucuronide (M6G, pharmacologically active and more potent than morphine) and morphine-3-glucuronide (M3G, neuroexcitatory, may cause myoclonus). In renal failure, M6G accumulates, leading to prolonged respiratory depression -- a crucial clinical consideration. Despite its essential status, access to morphine for pain relief in India has been historically restricted by complex NDPS Act regulations, though amendments in 2014 have improved availability. It remains the most important opioid in pharmacology examinations and the reference standard for analgesic potency comparisons.
Pharmacological class
Morphine belongs to the Opioid analgesic (natural opiate, phenanthrene class) class. Morphine is a full agonist at mu (mu-1, mu-2), kappa, and delta opioid receptors, with its primary analgesic effects mediated through mu receptors. It activates G-protein coupled receptors, inhibiting adenylyl cyclase, opening potassium channels (causing hyperpolarisation), and closing voltage-gated calcium channels (reducing neurotransmitter release). This results in inhibition of ascending pain pathways and alteration of pain perception at the cortical level.
Indian brand names and formulations
Available as: Morphine Sulphate Injection IP (Government supply), MS Contin (Mundipharma -- sustained release), Morcontin (Modi Mundi Pharma), Relivia (Cipla).
Injection (10 mg/mL, 15 mg/mL ampoules), Immediate-release tablets (10 mg, 20 mg), Sustained-release tablets (15 mg, 30 mg, 60 mg, 100 mg), Oral solution (10 mg/5 mL)
Regulatory status
Morphine is classified under Schedule H; also NDPS Act controlled substance in India under the Drugs and Cosmetics Act, 1940. Morphine is listed under Schedule H AND is a controlled substance under the Narcotic Drugs and Psychotropic Substances (NDPS) Act, 1985. Prescribing, dispensing, and stocking require NDPS licensing. The 2014 NDPS Amendment simplified state-level access for essential medical use.
Indications
- Severe acute pain (post-operative, trauma, burns)
- Acute myocardial infarction (reduces pain, anxiety, and preload)
- Cancer pain (WHO analgesic ladder step 3)
- Acute pulmonary oedema (reduces preload via venodilation)
- Chronic severe pain in palliative care
- Pre-anaesthetic medication
- Renal colic and biliary colic (with caution -- can cause sphincter of Oddi spasm)
Dosing
Acute pain: 2.5-10 mg IV/SC every 4 hours (titrate to effect). IM: 10 mg every 4 hours. Oral immediate-release: 5-15 mg every 4 hours. Oral sustained-release: 15-30 mg every 12 hours. Cancer pain: individualised titration with no ceiling dose for pure agonists. Renal impairment: reduce dose and extend interval (M6G accumulates). Elderly: start at 25-50% of standard dose. MI: 2-4 mg IV every 5-15 minutes until pain relief.
Contraindications
- Respiratory depression or severe bronchial asthma (unmonitored setting)
- Paralytic ileus
- Acute alcoholism and delirium tremens
- Head injury with raised intracranial pressure (masks neurological signs, raises ICP via CO2 retention)
- Concurrent MAO inhibitor use (risk of serotonin syndrome and respiratory crisis)
- Cor pulmonale
Adverse effects
- Respiratory depression (most dangerous; dose-related, mediated by mu-2 receptors in medullary respiratory centres)
- Constipation (most common with chronic use; tolerance does NOT develop to this effect)
- Nausea and vomiting (stimulation of CTZ in area postrema)
- Miosis (pinpoint pupils -- diagnostic sign of opioid use/overdose)
- Urinary retention
- Pruritus (especially with neuraxial administration, due to histamine release)
- Hypotension (histamine release, reduced sympathetic tone)
- Physical dependence and addiction with prolonged use
- Biliary colic exacerbation (sphincter of Oddi spasm)
Drug interactions
- Benzodiazepines -- additive respiratory depression (FDA boxed warning)
- MAO inhibitors -- severe, potentially fatal interaction (serotonin syndrome, respiratory crisis)
- Phenothiazines (chlorpromazine) -- enhanced sedation and hypotension
- Rifampicin -- induces morphine glucuronidation, reducing efficacy
- Mixed agonist-antagonists (pentazocine, buprenorphine) -- can precipitate withdrawal in opioid-dependent patients
Pregnancy and lactation
Category C (D if used prolonged or at high doses near term). Crosses the placenta. Chronic use near term causes neonatal abstinence syndrome (NAS) -- irritability, seizures, tremors, poor feeding. Single doses for labour analgesia are generally safe if delivery is not imminent. Avoid in preterm labour (respiratory depression in premature neonate).
Exam-style clinical scenario
A 60-year-old man with chronic kidney disease (eGFR 15 mL/min) is given morphine for post-operative pain. Twelve hours later, he develops respiratory depression (RR 6/min) and pinpoint pupils. What is the explanation and management? Answer: Morphine-6-glucuronide (M6G), the active metabolite of morphine, accumulates in renal failure, causing delayed and prolonged respiratory depression. Management: IV naloxone (0.4-2 mg, repeat every 2-3 minutes) is the specific opioid antagonist. In CKD patients, fentanyl or hydromorphone (metabolites less active) are safer alternatives.
Cost in India
INR 20-50 per 10 mg ampoule (injection); sustained-release tablets INR 30-80 per tablet
Clinical governance
Author: MedNext Editorial Team. Clinical reviewer: Awaiting clinical review. Jurisdiction: India (Drugs and Cosmetics Act, 1940). Sources: CIMS India, Indian Pharmacopoeia. Publication state: Awaiting clinical review. Correction: Report errors at support@mednext.academy.
Frequently Asked Questions
Why does tolerance not develop to morphine-induced constipation?
Opioid receptors in the GI tract (predominantly mu receptors in the myenteric plexus) undergo much less desensitisation compared to CNS receptors. The constipating effect involves both reduced peristalsis and increased sphincter tone, mediated through local enteric nervous system opioid receptors that maintain their sensitivity. Patients on chronic morphine almost always require concurrent laxative therapy.
Why is morphine contraindicated in head injury?
Morphine causes respiratory depression, leading to CO2 retention, which causes cerebral vasodilation and raises intracranial pressure (ICP) -- dangerous in a patient with already elevated ICP. Additionally, morphine-induced miosis and sedation mask the neurological signs (pupil changes, consciousness level) used to monitor head injury progression, preventing early detection of herniation.
What is the WHO analgesic ladder and where does morphine fit?
The WHO three-step analgesic ladder for cancer pain management recommends: Step 1 (mild pain) -- non-opioid analgesics (paracetamol, NSAIDs); Step 2 (moderate pain) -- weak opioids (tramadol, codeine) plus non-opioids; Step 3 (severe pain) -- strong opioids (morphine is the prototype) plus non-opioids, with or without adjuvants. Morphine is the gold standard Step 3 agent.
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