information:extraction, structural:scholar_edition
Pharmacokinetics

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.