A stable-labeled internal standard suitable for quantification of desipramine in antidepressant testing methods by LC/MS or GC/MS for applications in clinical toxicology, forensic analysis, or urine drug testing. Desipramine is a tricyclic antidepressant (TCA) that is used to treat depression, and is also an active metabolite of imipramine. This drug is known by the trade names Norpramin® and Pertofrane®.