Morphine – Effects, Uses and Side Effects

What is Morphine?

Morphine is a naturally occurring opioid alkaloid derived from the latex of the opium poppy (Papaver somniferum). It belongs to the class of strong opioids and is one of the most effective analgesics known to medicine. Morphine has been used in clinical practice since the 19th century and remains the gold standard for the treatment of severe and chronic pain. It is included on the World Health Organization (WHO) List of Essential Medicines.

Indications – When is Morphine Used?

Morphine is prescribed for a variety of conditions involving severe pain:

• Cancer pain: Morphine is the drug of choice for strong tumor-related pain, particularly in palliative care settings.
• Postoperative pain: Following major surgery, morphine is frequently used to manage pain during recovery.
• Myocardial infarction (heart attack): Morphine can relieve acute chest pain and anxiety associated with a heart attack.
• Severe trauma: In emergency medicine, morphine is used for rapid pain relief following serious injuries.
• Breathlessness (dyspnea): In palliative medicine, morphine can also alleviate severe breathlessness.

Mechanism of Action

Morphine exerts its effects by binding to opioid receptors in the central nervous system (brain and spinal cord) and in peripheral tissues. The primary receptor types involved are:

• Mu-opioid receptors (μ): Primarily responsible for pain relief, sedation, and respiratory depression.
• Kappa-opioid receptors (κ): Involved in analgesia and sedative effects.
• Delta-opioid receptors (δ): Modulate mood and pain perception.

By activating these receptors, morphine inhibits the transmission of pain signals and significantly reduces pain perception in the brain. It can also produce feelings of well-being (euphoria), which accounts for its potential for dependence and misuse.

Dosage Forms and Administration

Morphine is available in several formulations:

• Oral tablets and capsules: Immediate-release and extended-release (modified-release) forms for ongoing pain management.
• Injectable solution: For intravenous or subcutaneous administration, commonly used in emergency and hospital settings.
• Suppositories and patches: Available for patients who cannot take oral medication.

Dosage is always individualized based on pain severity, body weight, and the overall health of the patient. Morphine is a controlled substance and can only be dispensed with a special prescription issued by a licensed physician.

Side Effects

Like all opioids, morphine can cause a range of side effects:

• Common: Nausea, vomiting, constipation, drowsiness, dizziness.
• Less common: Dry mouth, sweating, itching (pruritus), confusion, mood changes.
• Rare but serious: Respiratory depression (dangerously slow breathing), circulatory collapse, dependence.

Constipation is one of the most frequent and persistent side effects and occurs in nearly all patients on long-term morphine therapy. Unlike nausea, it does not tend to resolve on its own and must be actively managed with laxatives or other measures.

Dependence and Misuse Potential

Morphine carries a high potential for physical and psychological dependence. With prolonged use, tolerance can develop, meaning that higher doses are required to achieve the same effect. However, when used as medically directed and under close supervision, the risk of addiction is significantly lower than with non-medical use. Discontinuation of morphine must always be done gradually and under medical supervision to prevent withdrawal symptoms.

Contraindications

Morphine must not be used, or must be used only with extreme caution, in the following situations:

• Severe respiratory depression or significant lung disease
• Acute abdominal pain of unknown origin
• Head injury with raised intracranial pressure
• Severe liver or kidney impairment
• Concurrent use of monoamine oxidase inhibitors (MAOIs)
• Infants under one year of age (only with special precaution)

References

1. World Health Organization (WHO): WHO Model List of Essential Medicines, 23rd Edition (2023). Available at: https://www.who.int/publications/i/item/WHO-MHP-HPS-EML-2023.02
2. Wiffen P.J., Wee B., Derry S., Bell R.F., Moore R.A.: Opioids for cancer pain – an overview of Cochrane reviews. Cochrane Database of Systematic Reviews, 2017. DOI: 10.1002/14651858.CD012592.pub2
3. Brunton L.L., Hilal-Dandan R., Knollmann B.C. (eds.): Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition. McGraw-Hill Education, 2018.