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Cannabis and the Brain
Episode 614th February 2022 • Brain Beat • National Academy of Neuropsychology Foundation
00:00:00 00:42:06

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Dr. Peter Arnett, Immediate Past President of NAN, hosts the podcast this week and welcomes Dr. Igor Grant, who will be talking with us today about cannabis. Dr. Grant is a Distinguished Professor and Director of the HIV Neurobehavioral Research Program and the Center for Medicinal Cannabis Research at UCSD who has served as Chair of the UCSD Department of Psychiatry from 2014 to 2019. He's a neuropsychiatrist who graduated from the University of British Columbia School of Medicine and received specialty training in psychiatry at the University of Pennsylvania, and additional training in neurology at the Institute of Neurology in London. Dr. Grant's academic interests focus on the effects of various diseases on the brain and behavior, emphasizing neuropsychological translational studies in HIV and drugs of abuse. He has contributed to approximately 800 scholarly publications and is the principal investigator of several NIH studies. In addition, NAN has recognized Dr. Grant with the Nelson Butters Award for research contributions to clinical neuropsychology and the Distinguished Lifetime Contribution to Neuropsychology Award. Dr. Grant is the Past President of the International Neuropsychological Society, otherwise known as INS, which honored him with the Paul Satz INS Career Mentoring Award. In addition to all these accomplishments, he is also the Founding Editor of the Journal of the International Neuropsychological Society, otherwise known as JINTS.

In this episode, Dr. Grant tells us about the history of the Center for Medicinal Cannabis Research and what it learned about the specific diseases or conditions that can be aided by cannabis. He provides insight into anecdotal evidence that THC was useful in diabetes and HIV/AIDS patients for relieving neuropathic pain. Dr. Grant, however, expresses concern over the long-term durability of this effect because the studies were relatively short-term. He comments on the proportion of THC used in different interventions, the regulations surrounding cannabis, which is considered a Schedule I drug, and gives an example of guidelines a typical doctor should follow when deciding to use cannabis.

Dr. Grant then talks about the benefits and risks of medical cannabis, sharing its impact on cognitive function if one already has a dementing disorder and preexisting anxiety or depression. He sheds light on his ongoing research and funding sources for research and elaborates studies of cannabidiol on people with early psychotic symptoms. Dr. Grant reveals that CBD and THC may help in breaking addiction. Other studies Dr. Grant delves into include one to help people with sleeping disorders and autism, a NIDA -supported study looking at kids experimenting with drugs from age 9 and following them through teen and early childhood, the dynamics and effects of abstinence, and the impact of cannabis on driving safety. Finally, he addresses gaps in our knowledge of cannabis that need to be pursued and impediments to research and discoveries in cannabis.

Episode Highlights:

  • The history and work of the Center for Medicinal Cannabis Research

  • Diseases or conditions that can be aided by cannabis

  • Benefits of marijuana to patients with HIV/AIDs and diabetes

  • The role of THC in managing neuropathic pain

  • Cannabis regulations

  • Guidelines for doctors to determine whether to prescribe cannabis

  • Risks and benefits of medical cannabis

  • The impact of THC on the cognitive function of a person with a dementing disorder

  • The dynamics and effects of taking THC with preexisting anxiety and depression

  • Dr. Grant's ongoing research

  • Sources of funding for research

  • A study on cannabidiol in people with early psychotic symptoms

  • How CBD helps in addiction treatment

  • Measurable cognitive impairments in recreational users

  • The dynamics, effects, and studies of abstinence
  • Cannabis and driving safety

  • Gaps in our knowledge of cannabis that need to be pursued

  • Impediments to cannabis research and studies


"There was a lot of anecdotal evidence that neuropathic pain, which is a kind of chronic, painful condition, with hypersensitivity and so forth, that maybe marijuana was useful, in that our patients with HIV AIDS that we were studying as part of a different program, were reporting this consistently."

"Those early studies did show that THC-containing products were helpful, at least in the short term, in managing neuropathic pain. And that's been confirmed in many studies in other places as well."

"Cannabis continues to be a Schedule I drug, which means basically that it's something that's classified with other compounds that are very dangerous and for which there isn't appropriate medical information of benefit. By the way, the latter is definitely not true anymore, but it's still sitting there."

"In the state of California, we have worked with our medical board to develop kind of a decision tree to guide physicians in whether or not in the first instance to even consider medicinal cannabis."

"In our state, it's legal. But you have to understand at the federal level, it's not legal. So doctors in California, for example, cannot write a prescription. They could lose their DEA registration, which would really impair their medical practice. So there's this gray area all the time."

"What I would just say informally is that we find that relatively low concentrations of THC appear to be helpful, so you don't have to get stoned."

"That doesn't mean it's 100% safe. No medicine is, right?"

"In older people, THC can increase heart rate. It can change blood pressure. So if you are a patient with serious heart disease, even these smaller or modest doses of THC could be harmful. Again, the studies have not been extended to large groups of older people with comorbid conditions."

"If you have a dementing disorder, certainly THC, like any other kind of drug that impairs, could impair cognitive function, could make it significantly worse."

"It is true that THC can produce anxiety in some people. It's a minority, but that's a known side effect and has been reported by speaking to people smoking marijuana that they get very anxious, get a panic attack even and so forth."

"Cannabidiol doesn't have many bad side effects the way some of our antipsychotic drugs do.”

"Is it possible that CBD may help in addiction treatment? There's again some evidence that CBD may reduce the craving that addicted people or animals have."

"I was involved in a meta-analysis years ago where we found that once you looked at studies that examined people who were abstinent at least for a week or two or more, there were really essentially no differences in cognitive functioning. There was a very teeny effect that we observed on a memory measure."

"Then, a second larger meta-analysis was conducted about a decade later. And that had the benefit of having more studies where people were truly abstinent. And they found that once you looked at that subgroup, they found no effect at all, like any neurocognitive measure."

"There is no question, though, if you are stoned all the time as a kid, you're not going to learn as well; you're going to get behind. And there's no question that the kind of everyday function outcomes is not good. But whether that's due to brain injury is a whole other matter."

"The person who has used occasionally or rarely or even modestly, I think the likelihood that the marijuana is a factor in any neuropsych impairment is very low unless they're actually stoned."

"In my experience, it's going to be unlikely that marijuana itself is the explanation for a significant neuropsych. But it may contribute, especially if they're still under the influence."


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