Morphine

Description

Morphine is a naturally occurring opiate extracted from the opium poppy (Papaver somniferum). It is the most abundant and active alkaloid found in opium latex and the parent compound from which semi-synthetic opioids (such as diamorphine/heroin and hydromorphone) are derived.

In clinical medicine, morphine is regarded as the gold-standard analgesic against which all other pain-relieving opioids are benchmarked. Like other opioids, it acts directly on the central nervous system to relieve severe acute and chronic pain.

Morphine is subject to extensive first-pass metabolism in the liver: when taken orally, only 40–50% of the dose reaches the central nervous system. It is available in immediate-release liquids (such as Oramorph), modified-release tablets and capsules (such as MST Continus and Zomorph), and ampoules for clinical injection.

Pharmacology

Morphine acts predominantly as a full agonist at the µ-opioid receptor (MOR) distributed throughout the brain and spinal cord, mimicking endogenous endorphins and enkephalins. Binding to MOR inhibits the transmission of nociceptive (pain) signals and activates the brain’s reward pathway by stimulating dopamine release in the nucleus accumbens.

To a lesser extent, morphine also acts as an agonist at the κ-opioid (KOR) and δ-opioid (DOR) receptors, which contribute to spinal analgesia and sedation.

With repeated administration, µ-opioid receptors desensitise and downregulate, leading to rapid tolerance and physical dependence. Sudden cessation causes acute opioid withdrawal. In overdose, profound depression of the respiratory centres in the brainstem causes hypoxia and fatal asphyxiation, which can be reversed by the opioid antagonist naloxone (see our Naloxone guidance).

Harm Reduction

Morphine in Drug Treatment:

While methadone and buprenorphine are the primary licensed medications for opioid dependence in the UK, slow-release oral morphine is utilised in specialist clinical circumstances and in several European treatment systems for individuals who cannot tolerate standard substitution therapies. Clinicians must account for morphine’s much shorter half-life and lower oral bioavailability compared to methadone when calculating equivalent maintenance doses.

• Carry naloxone: Naloxone reverses morphine overdoses. Always carry a kit and ensure those around you know how to use it. Obtain free kits via our Naloxone page.
• Avoid mixing with depressants: Combining morphine with alcohol, benzodiazepines, pregabalin, or other sedatives creates a high risk of fatal respiratory depression.
• Do not crush slow-release tablets: Extended-release tablets (such as MST) contain binders, waxes, and polymers designed to release the dose over 12 hours. Crushing them destroys the slow-release mechanism, delivering a potentially lethal dose all at once (‘dose dumping’), and injecting crushed pills causes severe vein and lung damage.
• Start low and go slow: Always begin with a minimal test dose if using illicit or diverted preparations.
• Do not use alone: Ensure someone is present who can call 999 and administer naloxone if you become unresponsive.
• Tapering and withdrawal: Never stop taking morphine suddenly after chronic use. Seek medical advice to plan a gradual, manageable reduction schedule.

History

In 1804, German pharmacist Friedrich Wilhelm Sertürner successfully isolated the principal alkaloid from opium, naming it morphium after Morpheus, the Greek god of dreams. This marked the very first time an active alkaloid had been isolated from a medicinal plant.

The invention of the hypodermic needle in the 1850s transformed morphine into the world’s most widely used surgical painkiller. Its widespread use during the American Civil War and European conflicts led to the first recognised wave of modern intravenous opioid dependence (often called the ‘soldier’s disease’ or morphinism).

In 1874, English chemist C.R. Alder Wright boiled morphine with acetic anhydride to synthesise diacetylmorphine (heroin). Today, morphine remains on the World Health Organization’s List of Essential Medicines as an indispensable analgesic worldwide.

Law

Class A under the Misuse of Drugs Act 1971.
Schedule 2 under the Misuse of Drugs Regulations 2001 (lawful to possess with a valid medical prescription).

Possible offences

• Possession: Maximum sentence of up to 7 years imprisonment, an unlimited fine, or both (without a valid prescription).
• Possession With Intent To Supply (PWITS): Maximum sentence of up to life imprisonment, an unlimited fine, or both.
• Supply: Maximum sentence of up to life imprisonment, an unlimited fine, or both.
• Production: Maximum sentence of up to life imprisonment, an unlimited fine, or both.

For more detailed information on sentencing and rights, visit our Drugs Law section.