You can no longer lie. Scientists can tell now if your marijuana came from Mexico or grew in your apartment. A team at Alaska Stable Isotope Facility has developed an isotope-based method that can tell which region a marijuana sample comes from and if it grew indoors or out. In a few years, the researchers could make even a marijuana isotope map, acting like a fingerprint database.

"There are scientists already doing this for drugs like heroin and cocaine. The potential is there for being able to do this for marijuana as well." said Matthew Wooller, Alaska Stable Isotope Facility director.

The method is based on the stable isotope ratios of carbon, oxygen, nitrogen and hydrogen. Isotopes are atoms of the same elements that vary in the numbers of neutrons encountered in nucleus (this induces differences in their mass) and stable ones do not decay over time (those unstable or radioactive disintegrate over time).

A stable isotope ratio mass spectrometer detects the ratio of light and heavy isotopes in a sample, revealing the origin of a sample.

"The marijuana holds a signature of the environment that it used to be grown in. It is laid down in time and preserved in the materials that make up a plant." said Wooller.

Oxygen and hydrogen ratios indicate the water used by a plant while growing, thus the place of cultivation.

"Water in Alaska and other high latitudes generally has a larger proportion of light oxygen and hydrogen stable isotopes than water from locations at lower latitudes. Carbon tells another story. It can offer information on whether a plant was grown outdoors or inside. Nitrogen could provide even more information. The testing at the UAF facility is novel because, for each sample, scientists are taking the isotopic signatures of four elements, rather than for just a single one. We have the potential to create a precise chemical fingerprint." said Wooller.

The research started two years ago, and with a large pool of marijuana samples, the team can make a marijuana isotope map for Alaska and beyond.

"The project has potential to help police on multiple levels. From an evidentiary standpoint, it could tie a growing operation to marijuana seized on the street and offer evidence of both the production of marijuana and its distribution. The common denominator that people use as their defense is that (they) are growing it for their personal use only. If marijuana seized from a dealer, for example, matched that growing operation, it could counter such a defense," said Investigator Stephen Goetz at the UAF Police Department.

"It could also help the state's drug enforcement officials track the trafficking patterns of marijuana by comparing where the marijuana was grown to where it is seized. It could, theoretically, focus law enforcement's efforts on where to look for (growing operations.)" he added.