How to Test the Potency of Pot-Infused Foods

Eating a bag of THC-laced gummy bears may seem like a safer way of taking your medical marijuana than smoking a joint, but how do you know that you're actually getting the right dose? It turns out the labels on edible products—when they even exist—are often inaccurate, and testing is actually very hard to do.

Up to a quarter of medical cannabis users in the US get their dose from edible products such as oils, brownies or candies. In Canada, the Supreme Court ruled in June that patients should be allowed to ingest edible medical marijuana, too. But while the number of products and the places such products are sold continues to grow, the regulations that govern how edibles should be labelled vary between jurisdictions, and are often weak and poorly enforced.

In fact, the rules governing medical edibles in most US states are looser than those that cover recreational edibles in Colorado and Washington, said Ryan Vandrey, a psychiatrist who studies marijuana at Johns Hopkins University.

Vandrey and his colleagues wanted to see whether edible medical marijuana products actually contained the amounts of THC and other cannabinoids that they claimed. So they bought a variety of candies, baked good and drinks from dispensaries in Los Angeles, San Francisco and Seattle and tested them in a lab. They decided a label was accurate if the concentration of THC in the product was within 10 percent of what was claimed.

"By and large, they did not have the concentrations of THC advertised," said Vandrey. Of the 75 products tested, 60 percent had less THC, and 23 percent had more, than what their label claimed. Some had almost no detectable THC, while others had up to 50 percent more than what was on the label.

That's a big problem for patients, said Vandrey, because lower than expected levels could leave a life-threatening condition untreated, while higher ones run the risk of significant side effects. "If you can't trust the label, you can't get reliable dose effects," he said.

But the problem for manufacturers and regulators is that edible medical cannabis products are actually really hard to test, explained Jahan Marcu, director of research and development at Green Standard Diagnostics, a company that helps labs purify and test cannabinoids.

The standard equipment for this kind of testing is a highly accurate and sensitive bit of chemical analysis gear called a high-performance liquid chromatograph. It just wasn't really built to handle baked goods. "When this device was designed, no one in their wildest dreams thought 'let's put a cookie in this,'" he said. "That's a good way to get some downtime on your really expensive equipment."

Brownies, gummy bears and other edible products are full of sugars, fats and other junk that can gum up lab equipment, and the THC is not evenly distributed throughout the products, so testers can never really be sure that they have an accurate sample without using large amounts of expensive solvent to try and dissolve the whole thing.

To deal with this issue, Marcu uses a technique called cryo-milling, in which the product to be tested is frozen with liquid nitrogen or dry ice, and ground up in a special blender with abrasive diatomaceous earth—similar to what you put on your garden to deter snails. He then separates out the various chemical components using a technique called flash chromatography before testing just the cannabinoid components in the usual way.

This method uses far less solvent, and gives highly accurate results, said Marcu. He is now teaching commercial testing labs how to use the technique, in the hopes of improving quality standards in the whole medical cannabis industry.

Until the testing and enforcement regime improves, Vandrey wants limits on the edible market. "It needs to be constrained to three to four product types—capsules, oil, and maybe one or two food products—for which standard methods of manufacture and testing can be developed and validated," he said.

Correction 20/7: An earlier version of this article described Green Standard Diagnostics as Green Systems Diagnostics and has since been updated.

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