Mianserin is a tetracyclic antidepressant prescribed for the treatment of depression and is sold under the trade names Lumin and Tolvon. This internal standard is suitable for quantitation of mianserin levels in urine, serum, or plasma by LC/MS or GC/MS for urine drug testing, clinical toxicology, forensic analysis, or isotope dilution methods. This tetracyclic antidepressant functions as a noradrenergic and a specific serotonergic antidepressant with anxiolytic, hypnotic, antiemetic, orexigenic, and antihistamine effects.