This stable-labeled internal standard is suitable for quantification of tilidine levels in GC/MS or LC/MS testing methods for clinical toxicology, forensic analysis, urine drug testing, or isotope dilution applications. Tilidine is a synthetic opioid analgesic used mainly in Germany, Switzerland and Belgium for treatment of moderate to severe pain, both acute and chronic. While tilidine is considered a moderately-potent opioid, its active metabolite nortilidine possesses analgesic effects roughly equivalent to that of morphine.