Overview
Codeine is a widely prescribed opioid analgesic and antitussive (cough suppressant) medication. It is primarily indicated for the management of mild to moderate pain and for the symptomatic relief of dry, non-productive coughs. As a naturally occurring opiate derived from the poppy plant, it has been used for decades in various medical settings. Codeine is frequently formulated in combination with non-opioid analgesics, most notably paracetamol (acetaminophen) or ibuprofen, to provide synergistic pain relief and reduce the required dose of the opioid component.

Mechanism of Action
Codeine exerts its analgesic effects by binding to mu-opioid receptors in the central nervous system. However, codeine itself is a prodrug; its primary analgesic activity is dependent on its metabolic conversion into morphine by the liver enzyme CYP2D6. Once converted, it alters the perception of and emotional response to pain. Its antitussive action is achieved through direct suppression of the cough center located in the medulla oblongata of the brainstem, effectively reducing the urge to cough.

Dosage and Administration
For pain management in adults, the typical oral dose ranges from 15 mg to 60 mg every 4 to 6 hours as needed, up to a maximum of 360 mg per day. When used as a cough suppressant, lower doses (e.g., 10 mg to 20 mg every 4 to 6 hours) are generally sufficient. It is crucial to use the lowest effective dose for the shortest possible duration. Patients must be aware of the total paracetamol intake if taking combination products to avoid hepatotoxicity. Codeine should be taken with food to minimize gastrointestinal upset.

Side Effects and Risks
Common side effects of codeine include drowsiness, constipation, nausea, vomiting, and dizziness. Because it is an opioid, it carries significant risks of tolerance, physical dependence, and addiction with prolonged use. Overdose can lead to severe respiratory depression, coma, and death. A critical safety concern involves ultra-rapid metabolizers—individuals who convert codeine to morphine much faster than normal due to genetic variations in the CYP2D6 enzyme. This can result in dangerously high, potentially fatal morphine levels even at standard doses.

Contraindications
Codeine is strictly contraindicated in children under 12 years of age for any indication, and in children under 18 years following tonsillectomy or adenoidectomy, due to the severe risk of respiratory depression. It should not be used in patients with significant respiratory depression, acute asthma, or known hypersensitivity to codeine. Caution is strongly advised in elderly patients, those with impaired hepatic or renal function, and individuals with a history of substance abuse.

Pregnancy and Lactation
The use of codeine during pregnancy should be avoided unless clearly necessary, as prolonged use can lead to neonatal opioid withdrawal syndrome. Codeine is contraindicated during breastfeeding. The drug and its active metabolite, morphine, are excreted into breast milk. In mothers who are ultra-rapid metabolizers, breastfed infants can be exposed to dangerously high levels of morphine, which has resulted in fatal infant respiratory depression.