Narcotic Analgesics and Morphine Pharmacology: Mechanism & Uses

Posted on Oct 30, 2025 in Airports

Narcotic Analgesics: Definition and Classification

Definition of Opioid Analgesics

Narcotic analgesics, also known as opioid analgesics, are drugs primarily used to relieve moderate to severe pain by acting on the central nervous system (CNS). They mimic the action of endogenous opioid peptides (like endorphins and enkephalins) by binding to specific opioid receptors.

Key Characteristics

• Potent analgesic effect
• Potential for dependence and tolerance
• Depress respiratory centers at high doses
• Can cause euphoria, sedation, and constipation

Classification (Based on Source)

• Natural Opiates: Morphine, codeine (derived from the opium poppy)
• Semi-synthetic Opioids: Heroin, oxycodone, hydromorphone
• Synthetic Opioids: Fentanyl, methadone, tramadol

Opioid Receptor Types

• μ (Mu) Receptors: Responsible for analgesia, euphoria, respiratory depression, and dependence.
• κ (Kappa) Receptors: Associated with spinal analgesia, sedation, and dysphoria.
• δ (Delta) Receptors: Modulate mu receptor activity.

Pharmacology of Morphine: Mechanism and Effects

Introduction to Morphine

Morphine is the prototype opioid analgesic and a potent natural alkaloid extracted from opium. It primarily acts on μ-opioid receptors.

Mechanism of Action (MOA)

Morphine binds to μ-opioid receptors in the CNS and peripheral nervous system. This binding reduces the transmission of nociceptive (pain) signals through the following cellular actions:

• Inhibition of adenylate cyclase, leading to a decrease in cAMP levels.
• Opening of K⁺ channels (causing hyperpolarization).
• Inhibition of Ca²⁺ channels (which reduces neurotransmitter release).

Pharmacokinetics

Pharmacological Effects

CNS Effects

• Analgesia (pain relief)
• Euphoria (via the mesolimbic dopamine system)
• Sedation and drowsiness
• Respiratory Depression (dose-dependent; due to reduced sensitivity to CO₂)
• Cough Suppression (acts on the medullary cough center)
• Miosis (pinpoint pupils – a diagnostic sign of opioid overdose)

Gastrointestinal Effects

• Constipation (due to decreased GI motility and increased tone)
• Increased biliary pressure

Cardiovascular Effects

• Vasodilation (due to histamine release)
• May cause hypotension

Endocrine and Immune Effects

• Reduces levels of LH, FSH, ACTH, and cortisol.
• Can suppress immune function with chronic use.

Therapeutic Uses of Morphine

• Severe Acute and Chronic Pain (e.g., post-operative pain, cancer pain, myocardial infarction)
• Pulmonary Edema (relieves dyspnea)
• Pre-anesthetic Medication
• Cough suppression (rarely used now)

Adverse Effects

• Respiratory depression (most serious)
• Nausea and vomiting
• Constipation
• Urinary retention
• Tolerance and physical dependence
• Addiction and abuse potential

Contraindications

• Head Injuries (risk of raising intracranial pressure)
• Asthma or COPD (due to risk of respiratory depression)
• Pregnancy (risk of neonatal opioid withdrawal syndrome)
• Severe hepatic or renal impairment

Drug Interactions

• CNS Depressants (e.g., benzodiazepines, alcohol) → additive sedative effects.
• MAO Inhibitors → risk of serotonin syndrome.
• Anticholinergics → increased risk of constipation and urinary retention.

Summary Table: Morphine Key Facts

Note: This information is for educational purposes only. Consult a healthcare professional for medical advice.