Recreational use

Codeine is often used as a recreational drug. This is mainly due to its easy availability over the counter or on prescription in combination products (which, in certain countries, are scheduled lower than codeine as a single-agent). People use it in order to obtain the euphoric effects associated with use of opioids. Codeine-containing cough syrups are often taken whole by drinking the syrup; combination pills may be taken whole or crushed and mixed with water for faster absorption into the body, or the codeine may be extracted using methods like cold water extraction.

Therapeutic use of codeine falls in the category of 10-60 mg at once. The recreational dose of codeine is between 60 mg and 400 mg; a dose over 400 mg will be wasted, because the liver cannot metabolise any more than that amount at once. Since codeine is an inhibitor of its own cyp2d6 pathway, it is preferred to take the dose at one time instead of gradually over a period of time, with respect to cold water extracted codeine.[citation needed]. Codeine can be administered orally, rectally and by intramuscular injection. Codeine should never be insufflated (snorted), smoked, or injected intravenously.

In some countries, cough syrups and tablets containing codeine are available without prescription; some potential recreational users are reported to buy the aforementioned from multiple pharmacies as to not incur any suspicion. It is reported that in France, 95% of the consumption of Néo-codion cough preparation, containing codeine, can be attributed to non-medical use. A heroin addict may use codeine to ward off the effects of a withdrawal.

In the United Kingdom, Ireland, Australia, New Zealand, and Canada tablets which combine codeine and paracetamol (acetaminophen) are widely available, and these can be consumed at higher-than-recommended doses for recreational effect. In doing so, users run the serious risk of hepatotoxicity associated with large doses of paracetamol, so some try to extract the codeine from the paracetamol through various methods, the most common and simplest being cold water extraction. While the combination of codeine with paracetamol at higher-than-recommended doses can possibly cause hepatotoxicity (liver damage), combination with ibuprofen can result in kidney problems/failure and additional stomach pain and nausea, and combination with aspirin can lead to internal hemorrhaging, particularly gastrointestinal hemorrhage.

Codeine is also demethylated by reaction with pyridine to illicitly synthesize morphine. Pyridine is toxic and carcinogenic, so morphine produced in this manner may be particularly harmful.