Jenny L. Wiley, PhD, is often asked by friends if they should take medical marijuana for various conditions. She reminds them that she is not a doctor, but Wiley, a distinguished fellow of behavioral pharmacology at RTI International, a nonprofit research institute based in Research Triangle Park, North Carolina, said she does not judge those who do partake. “If I were dying of cancer, I’d probably try it,” she said.

But Dr Wiley cautions that, for medical purposes, there is little solid research showing exactly what medical marijuana can treat. “Particularly with the oil, there are a lot of purported uses, and if you talk to some avid users, you’ll find out it’s good for anything that ails you,” she said. “But scientific evidence doesn’t back it up. I’m not necessarily saying the claims are false, but the evidence is just not there.”

There are a small number of exceptions. For example, in June, the FDA approved Epidiolex, a formulation of cannabidiol (CBD), for treating severe seizures in patients aged 2 years and older. CBD oil is available via the internet and is sold in shops across the country. Medical marijuana has been legalized in many states, and the Drug Enforcement Administration has legalized it for use in clinical trials at a handful of universities nationwide. As a result, physicians may need to be familiar with the facts and fallacies of medicinal cannabis.

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Legal or not?

“It’s a confusing time for doctors thinking about this because of the differing laws and because science hasn’t caught up to the use of it … partially because of those laws,” Dr Wiley said.

Marijuana legally can be used recreationally in 10 states, and it has been approved for medical use in 23 more states, including more conservative ones like Missouri and Utah. More than half of all Americans say it should be legalized for medical use, according to an October Pew Research poll.

With few exceptions, cannabis is still illegal under federal law. The FDA still considers marijuana as a Schedule 1 drug, meaning it has “no currently accepted medical use and a high potential for abuse.” Thus, medical marijuana is technically illegal under federal law, even it if contains no tetrahydrocannabinol (THC), the psychoactive component of cannabis. 

“Lots of people have been saying that CBD is now legal, but it technically is not,” Wiley said. “But it’s important to know the laws in each state, because they are all going to vary.”


Wiley said it is pretty well accepted that CBD, without THC, “is not likely to hurt you.” But there are a couple of things physicians should consider before prescribing. First, some liver enzymes that metabolize CBD also metabolize other drugs, so CBD has the potential to interact with other medications, Dr Wiley said.

Second, sourcing can be an issue, given the absence of federal regulations regarding the safety or packaging of CBD products. Although independent testing facilities exist, there are no regulations to govern their testing policies. Consequently, patients would not know exactly what’s in the product they are getting.

In a 2017 research letter published in the Journal of the American Medical Association, researchers purchased an array of CBD products available online. They sent the products to a laboratory to test for CBD and THC content. The researchers found that 42% contained more CBD than the label said, 26% had lower concentrations, and 31% were labeled accurately.

Of the 84 products tested, 18 had at least some THC. The levels were small, but “if you are giving it to child, it can be an issue,” Wiley said.

Contamination can also be a problem. Dr Wiley said she knows of at least 1 case in which CBD oil was found to contain fentanyl.

The other issue physicians need to understand is that writing a recommendation for medical marijuana is not like writing the usual prescription. There is no established dose and regimen, so patients decide on the product and how much to take. In some cases, the people staffing medical marijuana dispensaries wind up offering advice about how much medical marijuana to use, Wiley said.

She recommends telling patients to start at a low dose if a product has THC, especially if the medical marijuana is in edible form. The effects of smoking marijuana hit quickly, so people usually stop at a smaller dose. Edibles, however, can take up to 30 minutes before feeling the impact, she said. People can easily end up taking too much.

“You can overdose on THC, and while it won’t kill you, it will make you feel pretty bad,” she said. “People can have anxiety and other negative effects like panic attacks.”

Colorado had so many people overdosing on edibles, Wiley said, that they set packaging guidelines that went into effect in January to make the products safer for consumers.

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The evidence

Dr Wiley related that she attended a continuing education (CE) class on medical marijuana in which the presenter said THC could be used to treat anything, a statement she rejects. “If that’s what doctors are getting from CE, there is going to be an issue with these classes,” she said.

While the science is a bit up in the air, Wiley recommends a consensus study report released by the National Academies of Medicine in 2017 titled “The Health Effect of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research.” This provides an overview of the current knowledge of the efficacy and risks of cannabis use. According to the expansive article, there is some evidence that medicinal cannabis is effective at treating chronic pain, reducing chemotherapy-induced nausea and vomiting, reducing spasticity related to multiple sclerosis, improving sleep for people with obstructive sleep apnea, and some other conditions. They also found some evidence that it may decrease the risk of diabetes and metabolic syndrome (though they noted it may increase the risk of prediabetes).

Study authors also found little evidence linking cannabis smoking to lung cancer, but some data suggesting that it may trigger myocardial infarction and stroke.

Clinicians have some important factors to consider before recommending medical marijuana to patients, Dr Wiley said. First is the patient’s condition. Someone with stage 4 metastatic cancer who has received no relief from other pain treatments or a person with chronic pain seeking to avoid opioids may be candidates. However, caution should be exercised before recommending medicinal cannabis to a parent who wants a natural treatment for their child with leukemia. There are a host of chemotherapy regimens that – though they have unpleasant side effects – are very effective treatments.