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Pharmacology · Drugs and Prescriptions

Morphine hydrochloride

Morphinum hydrochloridi

Morphine hydrochloride is a benchmark narcotic analgesic belonging to the group of drugs affecting the central nervous system. As the principal opium alkaloid, the drug mimics the action of endogenous peptides and produces a potent analgesic effect coupled with a high risk of dependence.

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Dosage forms0.01 g tablets; 1% solution in 1 ml ampoules.
MechanismStimulation of opioid receptors (mimicking enkephalins).
Specific antidoteNaloxone (intravenously or intramuscularly).
Chemical naturePhenanthrene derivative, weak base (pKa 7.9).
How to write a prescription
Rp.: Tab. Morphini hydrochloridi 0,01
D.t.d. N 10
S. Внутрь по 1 таблетке 2-3 раза в сутки при сильных болях

Alternative prescriptions: Tabulettas Morphini hydrochloridi 0.01; Sol. Morphini hydrochloridi 1% - 1 ml; Tab. Morphini 0.01

Dosage form
Tab. 0.01 g; amp. solution 1% - 1 ml
Administration
Per os 0.01-0.02 g in powders, tablets, drops (maximum single dose per os 0.02 g); s.c. 1 ml of 1% solution (maximum daily dose s.c. 0.05 g)
Group
Agents affecting the central nervous system
3 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Origin and physicochemical properties

The drug is a phenanthrene derivative and accounts for about 10% of total opium mass. Although total chemical synthesis was achieved back in 1952, on an industrial scale Morphinum is still obtained by extraction from plant raw materials due to economic feasibility.

Chemically, it is a weak base (capable of accepting a proton). Its pKa value is 7.9, which is very close to the physiological pH of blood.

Pharmacodynamics and mechanism of action

The mechanism of action is based on the stimulation of opioid receptors. Exogenously administered morphine mimics the effects of endogenous opioid peptides (specifically, enkephalins).

The central effects of the drug are multifaceted:

  • Psychotropic effect: induction of euphoria (the emotional coloring of pain is altered, fear and tension are eliminated). This is associated with the stimulation of receptors in the mesolimbic and mesocortical systems.
  • Effects on the brainstem: stimulation of the trigger zone of the vomiting center clinically manifests as nausea and vomiting. Stimulation of the oculomotor nerve nuclei leads to pupil constriction (miosis), which is a crucial diagnostic sign. There is also a decrease in the excitability of the respiratory center.
  • Cardiovascular system: in the context of differential diagnosis, bradycardia is characteristic of morphine.
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Pharmacokinetics and metabolism

The biotransformation of the drug proceeds via two main pathways:

  1. Microsomal oxidation: involving enzymes of the endoplasmic reticulum (primarily the cytochrome P-450 system), N-oxidation and dealkylation of the molecule occur.
  2. Conjugation (biosynthetic reactions): the drug reacts with an endogenous substrate — glucuronic acid (glucuronidation) to form esters, thioesters, or amides.

Clinically important interaction: morphine acts as an inducer of P-glycoprotein. It increases the activity of this transporter protein, which accelerates the elimination of other medicinal substances (P-glycoprotein substrates) and reduces their therapeutic efficacy.

Acute poisoning and management

Overdose is accompanied by profound respiratory depression and pronounced miosis. The logic of therapy is based on two areas:

1. Detoxification (removal of the toxin):

  • Gastric lavage with a 0.05% potassium permanganate solution (causes chemical oxidation of morphine) or a suspension of activated charcoal in warm water (toxin adsorption).
  • Bowel cleansing: administration of a saline laxative strictly after lavage.

2. Restoration of vital functions:

  • Administration of a specific pharmacological antagonist — naloxone (an opioid receptor blocker) intramuscularly or intravenously.
  • In case of profound respiratory depression, resuscitation measures are indicated, including mechanical ventilation.

Prescription rules and dosages

The drug has a high addictive potential (causes drug dependence), so its dispensing is strictly regulated.

  • Per os: prescribed in powders, tablets, or drops at 0.01–0.02 g. The maximum single dose (MSD) per os is 0.02 g.
  • Parenterally: subcutaneously (s.c.), 1 ml of a 1% solution is administered. The maximum daily dose (MDD) for subcutaneous administration is 0.05 g.
How to memorize

Morphine constricts pupils (miosis), slows the pulse (bradycardia), and depresses respiration. Naloxone and gastric lavage with potassium permanganate are life-saving measures.

Class and exam questions

Why is the stomach washed with potassium permanganate solution in morphine poisoning?

The use of 0.05% potassium permanganate solution causes chemical oxidation of morphine, neutralizing its toxicity directly in the GI lumen.

How does morphine affect the pharmacokinetics of other drugs?

It is a P-glycoprotein inducer. This accelerates the elimination of drugs that are substrates of this transporter and reduces their clinical efficacy.

Which eye symptom indicates morphine intoxication?

Pronounced miosis (pupillary constriction). It occurs due to the specific stimulation of the oculomotor nerve nuclei.

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What else to study on this topic

  • Endogenous antinociceptive system and the role of enkephalins
  • Differences between narcotic and non-narcotic analgesics (NSAIDs)
  • Pharmacodynamics of naloxone as a competitive antagonist
  • The role of P-glycoprotein in drug-drug interactions
  • Mechanisms of physical and psychological opioid dependence

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