ManuscriptCarbon (δ13C) and nitrogen (δ15N) isotope ratios at natural abundance levels are useful tools in determining the region-of-origin for both cocaine and heroin. Here we show that cocaine originating from different geographic regions of South America exhibited pronounced differences in their δ13C and δ15N values. The distinct isotope-ratio combinations allow reliable determination of the region-of-origin for the major coca growing regions along the Andean Ridge
