Codeine phosphate is the phosphate salt form of codeine, a naturally occurring opioid alkaloid derived from the opium poppy (Papaver somniferum). It’s a prodrug metabolized in the liver (primarily by CYP2D6 enzyme) into morphine, which provides its main analgesic effects. Chemically, it’s C₁₈H₂₁NO₃·H₃PO₄, with a molecular weight of 406.37 g/mol.

Medical Uses

• Pain relief: Mild to moderate pain (e.g., post-surgical, dental). Often combined with acetaminophen (e.g., Tylenol #3) or ibuprofen.
• Cough suppression: Antitussive in syrups (e.g., for dry coughs).
• Antidiarrheal: In low doses (e.g., as part of Lomotil with diphenoxylate).
  Doses typically range from 15–60 mg every 4–6 hours for adults (max 360 mg/day), but ultra-rapid CYP2D6 metabolizers may experience toxicity at standard doses.

Pharmacology

Side Effects & Risks

• Common: Drowsiness, constipation, nausea, dizziness, itching.
• Serious: Respiratory depression (dose-dependent; risk highest >200 mg/day), addiction/dependence, overdose (pinpoint pupils, coma).
• Contraindications: Respiratory depression, acute asthma, paralytic ileus, children <12 (FDA black box for cough/cold due to apnea risk), breastfeeding (morphine in milk).
• Interactions: CYP2D6 inhibitors (e.g., fluoxetine) reduce efficacy; sedatives/alcohol amplify depression.

Legal Status
Schedule II controlled substance in the US (high abuse potential); prescription-only worldwide. Overdose treated with naloxone.

Evidence Base

• WHO Essential Medicines List (analgesic).
• Studies (e.g., Cochrane reviews) show modest efficacy for pain/cough vs. placebo, inferior to stronger opioids like morphine.
• Genetic testing recommended for poor/ultra-rapid metabolizers (e.g., ~10% Caucasians poor; 1–2% ultra-rapid).

Fun Fact: Codeine was first isolated in 1832 by Pierre Jean Robiquet. Recreational use often involves extraction from OTC combo pills (e.g., “lean” with promethazine), but purity varies wildly.

Warnings:

• Illegal Sources: Dark web, street dealers, or unregulated foreign sites (e.g., from India/Mexico) risk counterfeits, fentanyl contamination, arrest, or death. US penalties: Up to 20 years prison/fines for trafficking.
• Global Trends: Interpol/FDA seize millions in illicit shipments yearly; purity often <50%.
• Safer Alternatives: For pain—ibuprofen/acetaminophen; cough—dextromethorphan (OTC).

Not medical/legal advice—check local laws (e.g., DEA.gov, EMA.europa.eu). If you need it for health reasons, talk to a doctor.