10,11-Dihydro-10,11-dihydroxy Carbamazepine, a metabolite of the anticonvulsant carbamazepine and the antiepileptic prodrug oxcarbazepine, is produced through the biotransformation of carbamazepine via a carbamazepine 10,11-epoxide intermediate by epoxide hydrolase, and from oxcarbazepine via a 10,11-dihydro-10-hydroxy carbamazepine intermediate. This compound has been detected in wastewater effluent, highlighting its environmental presence following pharmaceutical use.