Dr. Adie Rae, neuroscientist, and scientific adviser to Weedmaps, made the distinction between infrequent cannabis use and regular cannabis use, which may have very different effects on the brain. The available research supports the notion that occasional cannabis use may have neuroprotective effects on the brain. In contrast, the effects of frequent cannabis use are less clear but could be negative.
Rae shared, "The only evidence I could find in the literature of neurotoxicity to brain cells is caused by synthetic cannabinoids (such as Spice and K2). Plant-based cannabinoids appear to do the opposite, at least in the short term."
Many of the cannabinoids in cannabis (especially CBD and CBG but THC as well) are actually neuro-protective, according to Rae. "That means they turn on healthy cellular processes like anti-oxidation, rather than stimulating the cellular processes that lead to cell death. Being neuro-protective is what makes cannabis and its derivatives attractive targets as therapies for degenerative brain disorders like Parkinson's and Alzheimer's,” she said.
One 2020 literature review published in Molecular Neurobiology indicated that THC and CBD could potentially be therapeutic for individuals with Parkinson’s and Alzheimer's disease.
A study performed on mice published in 2018 in Neurobiology of Aging showed that a very low dose of injected THC may trigger a reversal of Age-related cognitive impairments. The positive effects lasted seven weeks.
On the other hand, one study published in 2020 in the journal Addiction Biology showed that the total size of the hippocampus which is important for memory and learning, continues to get smaller with more frequent cannabis use “Cannabis isn't necessarily 'killing' brain cells, but there is clearly something that is not normal in the hippocampus of chronic cannabis users,” according to Rae.
In addition, some frequent cannabis users have reduced gray matter volume in several regions across the brain. Rae cited a 2020 study published in the scientific journal Neuroreport that demonstrated these gray matter changes in heavy cannabis consumers. "Again, this doesn't mean that cannabis is 'killing' these brain cells, but the areas are smaller than normal," Rae said. "Further, chronic cannabis use diminishes the production of key proteins that serve as survival tools for brain cells."
While studies have shown negative effects on the brains of frequent cannabis consumers, lower doses of THC may be beneficial.
“Because the endocannabinoid system is so involved in all of our cognitive and homeostatic processes, it's wise to use cannabis moderately and/or take regular breaks,” Rae said. She recommends at least 48 hours of abstinence at least once a month.
This advice, however, is for adult consumers, not those whose brains are still developing. “There are definitely developmental effects of cannabis on the developing brain, whether a person is in utero or in high school. The safest thing for brain health is to wait until the brain is fully developed, around age 22, before using cannabis," said Rae.
It would seem that, when it comes to cannabis consumption and brain health, less truly is more.
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