Olanzapine is one of the most widely used antipsychotic drugs, which acts as an antagonist for multiple neurotransmitter receptor sites. 2-Methyl-4-(4-methyl-1-piperazinyl)-10H-thieno [2,3-b][1,5] benzodiazepine (Olanzapine) labeled with carbon-14 in the four positions has been synthesized as part of a three-step sequence from 2-amino-5-methylthiophene-3-carbonitrile-[carbonitrile-14C].