Every so often, a package of marijuana arrives in Jason B. West’s mail at the University of Utah in Salt Lake City. While Dr. West may not be the only one on campus receiving deliveries of illegal drugs, he is probably the only one getting them compliments of the federal government.

Dr. West’s marijuana supply is decidedly not for consumption. It is meticulously cataloged and managed, repeatedly weighed to make sure none disappears, and returned to the sender (a laboratory at the University of Mississippi) or destroyed when he is done with it.

With financing from the Office of National Drug Control Policy, Dr. West, 34, is creating a model that can identify the geographic origin of cannabis plants based on certain chemical calling cards. The agency hopes to use the research to help decide where to concentrate its resources.

The research, the Marijuana Signature Project, relies on stable isotopes, which are forms of an element like nitrogen or oxygen, that have distinct atomic masses. Long employed in ecological research, stable isotopes are increasingly used for forensic purposes, including investigations into blood doping, arson and trafficking in contraband like drugs and endangered species.