L-Propoxyphene-d5 Hydrochloride is the isotope labelled analog and L-isomer of Propoxyphene Hydrochloride (P831500); a controlled substance (opiate) and analgesic (narcotic). The α-DL-and D-diastereoisomers possess marked analgesic activity in contrast to the β-diastereoisomers which are substantially inactive. Oral administration of L-Propoxyphene Hydrochloride enhances the analgesic activity of D-Propoxyphene Hydrochloride.