Codeine is a naturally occurring opioid alkaloid from the opium poppy same family as morphine and oxycodone, though significantly less potent. Used for mild to moderate pain and cough suppression, codeine is among the most widely prescribed opioids globally and among the most widely misused. In India, codeine containing cough syrups have been subject to significant regulatory attention given their misuse as a recreational drug.

How Codeine Works 

Codeine itself has weak affinity for opioid receptors. The liver enzyme CYP2D6 converts codeine into morphine, which acts on mu-opioid receptors reducing pain perception, suppressing the cough reflex via the medullary cough centre and producing analgesia, euphoria and respiratory depression at higher doses.

The CYP2D6 pathway creates significant individual variation. Poor metabolisers (present in some populations) produce little morphine and have minimal therapeutic effect. Ultra-rapid metabolisers convert codeine to morphine at higher-than-expected rates, producing dangerous accumulation even at standard doses that is a particular concern in children.

Medical Uses: Pain Relief and Cough Suppression

Common uses are:

• Pain: Codeine is used for mild to moderate pain where non-opioid analgesics have been inadequate. Typical doses are 15 to 60 mg every four to six hours frequently combined with paracetamol. 

• Cough: Codeine acts on the medullary cough centre to suppress the cough reflex. It remains one of the most effective antitussive agents for dry, non-productive cough. It is not appropriate for productive coughs, where cough suppression reduces secretion clearance and may worsen infection.

Codeine in Cough Syrups - How It Helps

Codeine phosphate in cough syrups (typically 10mg per 5mL) acts centrally to reduce the cough reflex, suppressing the symptom rather than treating the underlying cause. For dry, irritating post-viral or upper respiratory cough it provides meaningful symptomatic relief enabling sleep and reducing exhaustion.

In India, codeine-containing cough syrups are Schedule H drugs, requiring a prescription. Several states have imposed additional restrictions given the scale of misuse. 

Available Forms: Tablets, Syrup, Combination Products

Codeine is available as plain codeine phosphate tablets (15mg, 30mg), syrup (typically 10mg per 5mL) and fixed-dose combinations. The most common combination is with paracetamol for post-operative and musculoskeletal pain. Combination products with antihistamines and decongestants carry the same scheduling restrictions as plain codeine.

Side Effects of Codeine You Should Know About

Common side effects include:

• Constipation

• Nausea and vomiting

• Drowsiness

• Dizziness

• Dry mouth. 

Serious adverse effects at higher doses include:

• Respiratory depression 

• Hypotension

• Urinary retention

• Biliary spasm. 

Sedation increases with dose and can impair driving at therapeutic levels.

Risk of Dependency and Misuse

Codeine produces physical dependence. Tolerance develops within weeks; physical dependence (withdrawal syndrome on abrupt cessation) follows regular use of two or more weeks. Psychological dependence and compulsive drug-seeking characterise opioid use disorder, which codeine can produce.

Withdrawal symptoms include anxiety, restlessness, muscle aches, sweating, insomnia, diarrhoea, nausea and vomiting. Recreational misuse of codeine cough syrups often combined with alcohol or anxiolytics is a documented public health problem in India. Codeine should be used for the shortest duration and lowest dose.

Who Must Avoid Codeine?

Certain people should avoid codeine. They are:

• Children under 12: Codeine is contraindicated following international regulatory action as it may cause morphine toxicity in ultra-rapid metaboliser children. 

• Pregnancy: Not recommended in pregnancy, particularly in the third trimester when it may cause neonatal opioid withdrawal syndrome and respiratory depression in the newborn. 

• Breastfeeding: Codeine enters breast milk. In ultra-rapid metaboliser mothers, breast milk morphine concentrations can reach dangerous levels; neonatal deaths from this mechanism have been reported.

Codeine Interactions with Other Medicines

Key interactions are:

• CNS depressants like benzodiazepines, alcohol, sedating antihistamines and barbiturates

• CYP2D6 inhibitors like fluoxetine, paroxetine, quinidine and bupropion

• CYP2D6 inducers like rifampicin and some anticonvulsants

• MAO inhibitors 

• Opioid antagonists like naloxone, naltrexone.

Codeine vs Dextromethorphan – What's Safer for a Cough?

Dextromethorphan (DXM) is a non-opioid antitussive available without prescription in many cough formulations. It acts on sigma opioid and NMDA receptors to suppress the cough reflex without producing opioid-type dependence at therapeutic doses. For most adults with a dry cough, DXM is at least as effective as codeine with significantly lower risks of dependence and respiratory depression.

Codeine is preferred when cough is associated with pain including post-surgical cough, pleuritis or rib fracture. For otherwise healthy adults with a dry non-productive cough, DXM is the safer first-line antitussive. DXM has misuse potential at very high doses but is substantially safer at therapeutic doses.

Why Codeine Is a Controlled Substance in Many Countries

Codeine is a Schedule H drug in India, requiring a prescription. The reason comes down to how the body processes it, codeine converts into morphine, producing opioid effects that carry a real risk of misuse, dependence and addiction. Cough syrups containing codeine were, for a long time, widely misused simply because they were so easy to get hold of. There's also a serious safety concern when codeine is combined with alcohol or other medicines that slow down the central nervous system; this combination can cause severe breathing problems and in some cases, prove life threatening. In response to rising reports of misuse & addiction the Central Drugs Standard Control Organisation (CDSCO) tightened regulations to ensure codeine is prescribed and dispensed more safely.

Conclusion

Codeine is a medically legitimate opioid with a well-established role in mild to moderate pain and dry non-productive cough. Within appropriate dose, duration and patient selection its safety profile is acceptable when the alternative is undertreated pain or debilitating cough. Dependence, misuse and respiratory depression are serious risks underpinning its controlled status. Prescribers should inform patients of the five day analgesic guidance, the importance of not combining with alcohol or sedatives and non-opioid alternatives for most cough indications.

FAQs

1. What is codeine syrup used for?

   Codeine syrup suppresses dry, non-productive cough that is irritating and persistent but not bringing up sputum. It is not appropriate for productive coughs where mucus clearance matters.

2. Is codeine found in normal cough syrups?

   Yes in prescription cough syrups. Codeine-containing syrups are Schedule H drugs in India, requiring a prescription. Many over the counter cough syrups contain dextromethorphan or pholcodine instead.

3. Can children take codeine for a cough?

   Codeine is contraindicated in children below 12 and not recommended in those below 18 following tonsillectomy or adenoidectomy. Some children convert codeine into morphine more rapidly than others (ultra-rapid metaboliser) which can lead to dangerously high morphine levels and serious breathing problems. Because of these safety concerns regulatory authorities have restricted the use of codeine for treating cough and cold symptoms in children. 

4. Is codeine addictive?

   With regular use physical dependence develops within two weeks; tolerance to analgesic and euphoric effects drives dose escalation. Opioid use disorder including psychological dependence & compulsive use can develop particularly in those with prior substance use or mental health history.

5. What does codeine feel like when taken?

   At therapeutic doses codeine causes mild analgesia, cough suppression, drowsiness and mild relaxation. Some individuals experience nausea with the first dose. At higher doses, euphoria and more pronounced sedation occur. 

6. How long does codeine take to stop a cough?

   Onset: 30 to 60 minutes after oral administration. Peak antitussive effect within one to two hours; duration four to six hours per dose. Codeine should be used for the minimum duration necessary typically three to five days.

7. Why is codeine a controlled drug?

   Codeine produces genuine opioid effects via conversion to morphine, carries dependence potential and can cause respiratory depression and life threatening conditions in overdose or combination with alcohol and sedatives. 

8. Can codeine make you constipated?

   Yes the most consistent and predictable adverse effect of codeine. Constipation does not diminish with continued use. Anyone taking codeine regularly for more than a few days should proactively use a stimulant laxative.

9. Is codeine safe during pregnancy or breastfeeding?

   In pregnancy codeine risks neonatal withdrawal syndrome and respiratory depression in the newborn. In breastfeeding, ultra-rapid metaboliser mothers can produce breast milk with dangerously high morphine concentrations; neonatal deaths from this mechanism have been documented.

10. What is the difference between codeine and tramadol?

    Both are opioids for mild to moderate pain with dependence potential. Tramadol additionally inhibits serotonin and noradrenaline reuptake - a broader mechanism but with serotonin syndrome risk absent from codeine. Tramadol is also a CYP2D6-dependent prodrug. Neither has antitussive activity equivalent to codeine.

References

1. Pathan H, Williams J. Basic opioid pharmacology: an update. Br J Pain. 2012;6(1):11–6. https://doi.org/10.1177/2049463712438493

2. Crews KR, Gaedigk A, Dunnenberger HM, et al. Clinical Pharmacogenetics Implementation Consortium guidelines for cytochrome P450 2D6 genotype and codeine therapy: 2014 update. Clin Pharmacol Ther. 2014;95(4):376–82. https://doi.org/10.1038/clpt.2013.254

3. World Health Organization. Codeine and its salts — critical review. WHO Expert Committee on Drug Dependence, 34th report. 2006. https://www.who.int/medicines/areas/quality_safety/34th_ECDD_Critical_Review_Codeine.pdf

4. Madadi P, Koren G. Pharmacogenetic insights into codeine analgesia: implications to pediatric codeine use. Pharmacogenomics. 2008;9(9):1267–84. https://doi.org/10.2217/14622416.9.9.1267

5. Bhatt DL, Scheiman J, Abraham NS, et al. ACCF/ACG/AHA 2008 expert consensus document on reducing the gastrointestinal risks of antiplatelet therapy and NSAID use. Circulation. 2008;118(18):1894–909. https://doi.org/10.1161/CIRCULATIONAHA.108.191087