Codeine's analgesic effect is primarily due to its conversion to which active metabolite?

Codeine's analgesic effect is primarily due to its conversion to which active metabolite?

• A. Hydromorphone
• B. Norcodeine
• C. Morphine
• D. O-desmethyltramadol

Answer: (C)

Codeine's pain relief comes mainly from its transformation into morphine in the liver by the enzyme CYP2D6. Morphine is the active compound that binds mu-opioid receptors to produce analgesia, so it is the metabolite responsible for most of codeine's effect. Other possible metabolites exist, but they do not drive the primary analgesic action: norcodeine is not a major active contributor, hydromorphone is a downstream metabolite, and O-desmethyltramadol is the active metabolite of tramadol, not codeine. Genetic differences in CYP2D6 activity explain why people may have very different responses to codeine.

Codeine's pain relief comes mainly from its transformation into morphine in the liver by the enzyme CYP2D6. Morphine is the active compound that binds mu-opioid receptors to produce analgesia, so it is the metabolite responsible for most of codeine's effect. Other possible metabolites exist, but they do not drive the primary analgesic action: norcodeine is not a major active contributor, hydromorphone is a downstream metabolite, and O-desmethyltramadol is the active metabolite of tramadol, not codeine. Genetic differences in CYP2D6 activity explain why people may have very different responses to codeine.