The most commonly used are the hydrochloride (freebase conversion ratio 0.805, i.e. 10mg of the hydrochloride salt is equivalent in effect to 8.05mg of the freebase form), phosphate (0.736), sulphate (0.859), and citrate (0.842). Others include a salicylate NSAID, codeine salicylate (0.686), a bromide (codeine methylbromide, 0.759), and at least five codeine-based barbiturates, the phenylethylbarbiturate (0.56), cyclohexenylethylbarbiturate (0.559), cyclopentenylallylbarbiturate (0.561), diallylbarbiturate (0.561), and diethylbarbiturate (0.619). The latter was introduced as Codeonal in 1912, indicated for pain with nervousness. Codeine methylbromide is also considered a separate drug for various purposes.Codeine and morphine, as well as opium, were used in an attempt to treat diabetes in the 1880s and thereafter, as recently as the 1950s. Society and culture
Names
It is often sold as a salt in the form of either codeine sulfate or codeine phosphate in the United States, United Kingdom and Australia. Codeine hydrochloride is more common worldwide and the citrate, hydroiodide, hydrobromide, tartrate, and other salts are also seen. The chemical name for codeine is morphinan-6-ol, 7,8-didehydro-4,5-epoxy-3-methoxy-17-methyl-, (5α,6α)-

Recreational use
A heroin (diamorphine) or other opiate/opioid addict may use codeine to ward off the effects of withdrawal during periods where their preferred drug is unavailable or unaffordable.Codeine is also available in conjunction with the anti-nausea medication promethazine in the form of a syrup. Brand named as Phenergan with Codeine or in generic form as promethazine with codeine, it began to be mixed with soft drinks in the 1990s as a recreational drug, called syrup, lean, or purple drank.
CYP3A4 produces norcodeine, and UGT2B7 conjugates codeine, norcodeine, and morphine to the corresponding 3- and 6-glucuronides. Srinivasan, Wielbo and Tebbett speculate that codeine-6-glucuronide is responsible for a large percentage of the analgesia of codeine, and thus these patients should experience some analgesia. Many of the adverse effects will still be experienced in poor metabolizers. Conversely, between 0.5% and 2% of the population are "extensive metabolizers"; multiple copies of the gene for 2D6 produce high levels of CYP2D6 and will metabolize drugs through that pathway more quickly than others. Some medications are CYP2D6 inhibitors and reduce or even completely block the conversion of codeine to morphine. The best-known of these are two of the selective serotonin reuptake inhibitors, paroxetine (Paxil) and fluoxetine (Prozac) as well as the antihistamine diphenhydramine (Benadryl) and the antidepressant bupropion (Wellbutrin, also known as Zyban). Other drugs, such as rifampicin and dexamethasone, induce CYP450 isozymes and thus increase the conversion rate. CYP2D6 converts codeine into morphine, which then undergoes glucuronidation. Life-threatening intoxication, including respiratory depression requiring intubation, can develop over a matter of days in patients who have multiple functional alleles of CYP2D6, resulting in ultrarapid metabolism of opioids such as codeine into morphine.Studies on codeines analgesic effect are consistent with the idea that metabolism by CYP2D6 to morphine is important, but some studies show no major differences between those who are poor metabolizers and extensive metabolizers.