Norhydrocodone is the major metabolite of the opioid analgesic hydrocodone. It is formed from hydrocodone in the liver via N-demethylation predominantly by CYP3A4. Unlike hydromorphone, a minor metabolite of hydrocodone, norhydrocodone is described as inactive. However, norhydrocodone is actually an agonist of the μ-opioid receptor with similar potency to hydrocodone, but has been found to produce only minimal analgesia when administered peripherally to animals. This is likely due to poor blood-brain-barrier and thus central nervous system penetration.
See also Norbuprenorphine Norbuprenorphine-3-glucuronide Normorphine Noroxymorphone
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