Well, you’ll be relieved to learn that the simple answer is no, weed doesn’t kill brain cells. At least, there’s no evidence that it does, according to Adie Rae, an assistant scientist at the Legacy Research Institute in Portland, Oregon, and cofounder of Smart Cannabis, a company dedicated to identifying the world’s best cannabis flower.
On the contrary, Rae says plenty of scientific evidence suggests that cannabinoids “are actually neuroprotective,” which is why cannabis research is currently focused on treating Parkinson’s and Alzheimer’s disease.
There are, however, a few caveats, one being that synthetic cannabinoids are undoubtedly neurotoxic. Moreover, Rae emphasizes that weed loses its neuroprotective abilities when ingested by someone whose brain is still developing (namely, if you’re under 25). That doesn’t mean it kills brain cells, per se, but it impedes your neurological development, which can negatively impact your reasoning and mood. Studies frequently highlight the underdevelopment of adolescent user’s hippocampus, a region of the brain that plays a major role in learning and memory.
Likewise, while there are conflicting studies, Rae says some suggest that “chronic, heavy” cannabis users have less gray matter in certain brain areas (the hippocampus is one of them). Again, this doesn’t necessarily mean that weed is killing brain cells, but it does suggest that the plant is causing some abnormalities.
These days, “chronic and heavy” are hard to define because everyone and their mother smokes weed, but Rae says if you’ve developed a decent tolerance, “you can stand to take a break.” In other words, if you don’t feel anything after a couple puffs of 30-percent flower, put the joint down for a few days. Likewise, the studies in question typically focus on daily smokers, so keep your smoking frequency in mind.
On a final note, it’s important to realize that our understanding of weed is still evolving. For example, a 2012 study from New Zealand made headlines when it found that adolescent stoners lost an average of six to eight IQ points. Then, a 2013 response to the study argued that personality factors like conscientiousness played a role in the reported cognitive decline. Meanwhile, a longitudinal twin study from 2016 claimed that genetic factors are to blame for cognitive decline, not weed. Another 2016 study found no evidence whatsoever that adolescent marijuana use leads to a decline in intelligence. In short, the science is uncertain.
Still, we can relatively safely conclude that so long as your brain is developed and you’re not smoking constantly, you’ll be more or less okay.