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Morphine: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 19, 2019.

1. How it works

  • Morphine is an analgesic (pain-reliever) that binds to mu opioid receptors in the brain and stomach. Morphine has very strong pain relieving effects and it may be used to relieve moderate-to-severe pain that is unresponsive to other, less potent, pain-relieving medicines.
  • Morphine belongs to the group of medicines known as narcotic analgesics. It may also be called an opioid analgesic or an opioid.

2. Upsides

  • Relieves moderate-to-severe acute and chronic pain not controlled by other pain-relieving medicines.
  • Available as immediate release tablets, extended-release tablets and capsules, solutions and injections.
  • Generic morphine is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Nausea, vomiting, dizziness, blurred vision, rashes and sweating. Constipation caused by morphine may be severe and laxatives are typically required.
  • Drowsiness which may affect a person's ability to drive or operate machinery. Avoid alcohol at all times (alcohol can increase blood levels of the drug leading to a fatal overdose).
  • Rarely, serious, life-threatening, breathing problems may occur. The risk is greater with slow-release forms, in people with pre-existing respiratory disease, in seniors or the frail, or in those taking other medications that cause respiratory depression (such as benzodiazepines).
  • There is a large variability in the way different people respond to morphine.
  • Known to cause addiction and dependence; the risk is higher in people with disturbances in their mental health. May be misused and legitimate supplies of products containing morphine may be sought out by drug seekers.
  • Abrupt discontinuation of any morphine-containing medication in a person who has become physically dependent on it may lead to a withdrawal syndrome and symptoms such as restlessness, pupil dilation, watery eyes and a runny nose, sweating, muscle aches, insomnia, irritability and gastrointestinal complaints. Babies born to mothers who are physically dependent on morphine will also be physically dependent.
  • Interaction or overdosage may also cause serotonin syndrome. Symptoms include mental status changes such as agitation, hallucinations, coma, or delirium; a fast heart rate; dizziness; flushing; muscle tremor or rigidity; and stomach symptoms (including nausea, vomiting, and diarrhea).
  • May not be suitable for people with pre-existing respiratory depression or respiratory disease, with seizure disorders or a head injury, people with gastrointestinal obstruction, or who have recently taken monoamine oxidase inhibitors.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Morphine is a very effective pain reliever but commonly causes constipation and carries a high risk of addiction and dependence.

5. Tips

  • Report any breathing difficulties to your doctor immediately.
  • Do not drive or operate machinery or perform hazardous tasks if morphine makes you drowsy.
  • Avoid alcohol (may contribute to sedative and other adverse effects).
  • Laxatives may be needed to treat constipation and antiemetics may be used to relieve nausea.
  • Swallow slow-release forms whole; do not crush, chew, or attempt to dissolve. Slow-release forms should only be given to people requiring round-the-clock pain relief who have been trialed previously on immediate-release morphine.
  • Keep well out of reach of children; even one accidental dose can be fatal.
  • Be careful when measuring morphine solution to ensure the correct dosage is given.
  • Taper off dosage under medical supervision after extended administration as withdrawal symptoms may result.
  • Withdrawal symptoms (symptoms may include muscle and bone pain, diarrhea, insomnia, vomiting) may occur if long-term morphine is stopped abruptly; discontinue slowly on a doctor's advice.
  • Avoid alcohol while taking this medicine.
  • May lower blood pressure on standing; take your time when going from a lying down to a standing up position.
  • The need for continued treatment with morphine should be assessed at regular intervals.

6. Response and Effectiveness

  • The pain-relieving effects of morphine are usually seen within 60 minutes and may last up to 15 hours. The onset of effect and the duration of action depends on the formulation of morphine used.

7. Interactions

Medicines that interact with morphine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with morphine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with morphine include:

  • antidepressants, such as tricyclic antidepressants (eg, amitriptyline), monoamine oxidase inhibitors (eg, isocarboxazid, phenelzine, and tranylcypromine), or SSRIs (eg, fluoxetine, sertraline)
  • anticonvulsants, such as carbamazepine, phenytoin, phenobarbital, or primidone
  • antipsychotics (such as butyrophenones, phenothiazines, or thioxanthenes) and atypical antipsychotics (eg, olanzapine, quetiapine, ziprasidone)
  • any medication that may cause drowsiness, such as amphetamines, benzodiazepines (eg, diazepam, lorazepam), first-generation antihistamines (such as doxylamine or promethazine), metoclopramide, or opioids (such as codeine or oxycodone)
  • buprenorphine
  • cimetidine
  • diuretics, such as furosemide
  • ipratropium or other anticholinergics
  • isocarboxazid
  • muscle relaxants, such as baclofen or cyclobenzaprine
  • pentazocine.

Avoid drinking alcohol or taking illegal or recreational drugs while taking morphine.

Note that this list is not all-inclusive and includes only common medications that may interact with morphine. You should refer to the prescribing information for morphine for a complete list of interactions.


Morphine (systemic). Revised 07/2019.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use morphine only for the indication prescribed.

Copyright 1996-2021 Revision date: November 19, 2019.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.