N-Desmethylclozapine is an active metabolite of Clozapine, an atypical antipsychotic drug used for treatment of schizophrenia. Clozapine is sold under the trade names Clozaril and FrazaClo in the US. This Snap-N-Shoot^® stable-labeled internal standard is suitable for quantitation of N-desmethylclozapine levels in urine, serum, or plasma by LC/MS or GC/MS in clinical toxicology, forensic analysis, and urine drug testing applications.