A stable-labled internal standard suitable for quantitation of desipramine levels in urine, serum, or plasma by LC/MS or GC/MS for urine drug testing, clinical toxicology, forensic analysis, or isotope dilution methods. Desipramine is a tricyclic antidepressant (TCA) sold under the brand names Norpramin? and Pertofrane. This TCA drug is also a primary active metabolite of imipramine.