Study: Most marijuana edibles have mislabeled potency

Researchers from Johns Hopkins University did a study to see if the amount of THC in edible marijuana products was the same as the amount specified on the labels. The answer was a resounding “nah, man.”

Hopkins scientists went to Colorado and Washington state, where recreational marijuana is legal, and bought a total of 75 different edible products containing marijuana. They then tested the products’ THC content to see if it matched the amount of THC that was promised on their labels.

Marijuana edibles, via Wikimedia Commons

Marijuana edibles, via Wikimedia Commons

They found that over three three quarters of the edibles did not contain the specified amount of THC, with 60 percent of edibles tested containing less THC than advertised. 23 percent of the products actually contained more THC than was claimed on the label.

The researchers state that edibles containing marijuana cannot be relied upon to give a medicinal dose to patients taking it. One researcher said, “I suspected that we would see variability, but I was shocked at how much variability there was.”

One reason may be that both states require in-state testing of THC content by local labs. These labs, and labs in general, don’t have much experience in testing for THC in substances other than serum and urine. And testing for THC in marijuana plants and oils is more straightforward than trying to test for marijuana in, say, a brownie, where there are a number of other ingredients present.

For pharmaceuticals prescribed in the U.S., the Food and Drug Administration requires strict testing on drugs produced, including medications like PrEP and aspirin. But since the FDA states that marijuana is a non-medicinal drug, it has nothing to do with determining the purity or amount to THC in any marijuana products.

Another reason for the mislabeling is that the producers of medical marijuana edibles are mostly small mom and pop stores. They may not have the knowledge or skills to prepare brownies, cookies and other edibles properly or consistently. Recipes differ and how the THC is added to the mixture varies. Of course, there is also the possibility that there may be some producers who are just shortchanging the consumer to increase their own profits.

For right now at least, if you or someone you know is using medical marijuana and expecting a consistent dose, it may be much better to use it in a non-edible form.  Perhaps, over time the analytical techniques will get better, or the FDA will step in, and the THC content of edibles will be more accurate.


Mark Thoma, MD, is a physician who did his residency in internal medicine. Mark has a long history of social activism, and was an early technogeek, and science junkie, after evolving through his nerd phase. Favorite quote: “The most exciting phrase to hear in science... is not 'Eureka!' (I found it!) but 'That's funny.'” - Isaac Asimov

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