People who buy medical marijuana products might not be getting what they paid for, a study finds. And evidence remains elusive on benefits for most medical conditions, even though almost half the states have legalized medical marijuana.

The majority of edible cannabis products sold for medicinal purposes have labels that do not accurately reflect the amount of delta-9-tetrahydrocannabinol, THC for short, infused in them. THC is the component that's responsible for the marijuana high. But it's also known as dronabinol, a prescribed medication used to treat nausea and vomiting caused by chemotherapy.

THC and cannabidiol (CBD), another chemical component of cannabis, are believed to be primarily responsible for therapeutic benefits, especially when the THC: CBD ratio is close to 1:1, according to the study.

Of 75 products legally purchased in three cities, only 17 percent were correctly labeled, according to the report, which was published Tuesday in JAMA, the American Medical Association's journal. Accuracy for labeling was defined as the product having THC content within 10 percent of what's printed on the label.

Twenty-three percent were under-labeled, meaning there's more THC than advertised. Sixty percent were over-labeled, where customers were not getting the bang for their buck.

"A couple of products that were supposed to contain 100 milligrams of THC but had only two to three [milligrams]," lead author Ryan Vandrey, an associate professor of psychiatry and behavioral sciences at Johns Hopkins University says. "That was striking – these were not cheap products and were being sold as medicine."

Currently 23 states and Washington D.C. have laws legalizing marijuana for medical purposes. Four states and D.C. allow legal recreational use of cannabis. Some laws are broader than others, and qualifications for medical marijuana vary as well.

The rush to legalize medical marijuana tends to obscure the fact that it's not clear if medical marijuana has any therapeutic benefits at all. A review of studies on the topic, also published in Tuesday's JAMA, found "moderate" evidence that cannabinoids help with chronic pain and spasticity. But the researchers found little evidence that they help with nausea and vomiting due to chemotherapy, weight gain in people with HIV, sleep disorders, and Tourette syndrome. About one third of people in the studies reported side effects ranging from probably OK (euphoria) to distressing (vomiting, dizziness, hallucinations.)

Does this mean all the cannabis-infused tea that you've been drinking doesn't help your anxiety disorder at all? It's really impossible to say. There's just not enough scientific evidence to prove that they do work, or to tell us how much THC is needed to treat a certain condition.

For the people who are using medical marijuana to treat illnesses, the population affected by mislabeling is not small: an estimated 16 to 23 percent of medical cannabis patients consume edible products, according to the Vandrey study. Losing out on potential benefits is one thing, but potential overdosing poses a much bigger threat, especially when it comes to edibles. Undesirable side effects such as decreased short-term memory, panic, paranoia and even acute psychosis are possible, and the risk increases with higher dosages.

In the natural cannabis plant there is a ceiling amount of THC, but edibles can contain much more. . A pot-infused brownie with over 1200 milligrams of THC can look the same as the brownie with only 50 milligrams of THC.

Marijuana product testing, as Shots has previously reported, is a fairly new phenomenon. Oversight and regulations for testing medicinal cannabis varies from state to state.

Colorado mandated potency testing for marijuana edibles last May, but the rule only applies to edibles for recreational purposes.

As a result, labels for recreational marijuana are getting better at accurately stating THC content, according to Ian Barringer, owner of RM3 Labs in Denver, Colo. Products for both medicinal and recreational uses came in much weaker than labeled in earlier years, Barringer says, but most of the product the lab tests now fall within the acceptable range of 20 percent plus or minus the labeled THC content displayed on the label.

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