Does Weed Kill Brain Cells? And 5 Other Things to Know
We don’t know for sure if using marijuana can kill your brain cells.
More research is also needed to determine whether each form of use — including smoking, vaping, and ingesting edibles — has a different effect on your brain’s overall health.
Studies evaluating the cognitive effects of long-term marijuana use are ongoing.
Here’s what we currently know about how weed affects the brain.
A well-known 2012 study from New Zealand evaluated marijuana use and cognitive ability in more than 1,000 individuals over a 38-year period.
The researchers reported an association between ongoing marijuana use and cognitive decline.
In particular, they found that:
- People who started using marijuana heavily as adolescents and continued as adults lost an average of six to eight IQ points by the time they reached midlife.
- Among the group above, people who stopped using marijuana as adults didn’t regain lost IQ points.
- People who started using marijuana heavily as adults didn’t experience any IQ loss.
This study had a significant impact for a few reasons.
First, it was among the first large, longitudinal (long-term) studies to assess marijuana use and cognitive functioning.
Next, the results suggest that marijuana use during adolescence may have an irreversible effect on adolescent brain development. Some additional research supports this conclusion.
However, the New Zealand study also has significant limitations.
For one, it isn’t possible to conclude that marijuana use causes lower intelligence based on this study alone.
While the researchers controlled for differences in participant education levels, they didn’t rule out additional factors that may have contributed to cognitive decline.
A 2013 reply to the New Zealand study suggests that personality factors may play a role in both marijuana use and cognitive decline.
The author cited conscientiousness as an example. Low conscientiousness might explain both drug use and poor performance on tests of cognition.
Genetic factors may also contribute to cognitive decline, as suggested by a longitudinal twin study from 2016.
In this case, the researchers compared changes in IQ between twins who used marijuana and their abstinent siblings. They didn’t find any significant differences in IQ decline between the two groups.
The key takeaway? More research needs to be done to understand how marijuana use affects intelligence over time.
Researchers haven't determined whether smoking weed kills brain cells, but that hasn't stopped some groups from comparing the substance to nicotine and alcohol, two established brain cell killers. Here's what the science actually says about marijuana's effects on the brain, which users are most at risk, and more.