codein

Codein is a term most commonly associated with codeine, an opioid analgesic and antitussive used to treat mild to moderate pain and to relieve cough. Codeine occurs naturally in opium in small amounts and is typically manufactured for medical use in purified form, often in combination products with acetaminophen (paracetamol) or nonsteroidal anti-inflammatory drugs. It was first isolated in 1832 by French chemist Pierre Robiquet.

Pharmacology and metabolism: Codeine acts as a prodrug; after ingestion, a portion is metabolized in the liver by the enzyme CYP2D6 into morphine, which contributes much of the analgesic effect. Genetic differences in CYP2D6 activity produce a range of metabolizer phenotypes from poor to ultra-rapid. Ultra-rapid metabolizers can experience higher morphine exposure and an increased risk of serious adverse effects, including respiratory depression. Codeine can also cause drowsiness, dizziness, and constipation, and its rewarding properties may lead to dependence with prolonged use.

Medical uses and administration: It is prescribed for short-term relief of mild to moderate pain and, in some formulations, for cough suppression. In many regions, codeine is available only in combination products and may be restricted in duration of use, age groups, or dose. Its effectiveness for cough is variable and it is not recommended for chronic cough.

Safety and regulatory considerations: Common adverse effects include sedation, nausea, and constipation. Serious risks include respiratory depression, particularly in young children, people with respiratory conditions, or those who are rapid metabolizers. Dependence and withdrawal can occur with prolonged use. Regulations vary by country, with codeine often classified as a controlled substance and subject to prescription or dispensing limits, including additional restrictions for pediatric use and in breastfeeding.

See also: codeine-related regulations, metabolism variations.