Thanks to Dr. Sherry Yafai for forwarding Marijuana and the hippocampus: A longitudinal study on the effects of marijuana on hippocampal subfields. It was posted February 28 2020 by Progress in Neuro-Psychopharmacology and Biological Psychiatry. We boldfaced two sentences in the abstract and asked Dr. Yafai to confirm that growth in these subfields is a good thing.  Her reply is below the graphic.


• First study to check the effect of cannabis usage on hippocampus at subfields level.

• Uses a longitudinal approach with FreeSurfer.

• Persistent usage of cannabis did not result in atrophy of the subfields over time.

• Certain subfields showed an increase in the volume in cannabis users.


The psychoactive effects of cannabis, one of the most commonly used narcotics, have been documented extensively. Despite multiple studies being undertaken, there have been only a few longitudinal studies investigating the effect of long term usage of cannabis on various subcortical structures. This study aims at looking deeper into the effects of long term usage of cannabis on different hippocampus subfields.1 Participants were split into two groups, cannabis users and healthy controls. All the test subjects filled out the Cannabis Usage and Disorder Identification Test (CUDIT) and underwent T1-structural MRI scans twice, at a baseline and a followup 3 years later. The subfield volumes were measured using the software package Freesurfer with the LongitudinalHippocampalSubfields (v6.0) Module. Lifetime usage in grams was calculated for each participant until baseline and followup, independently, using linear interpolation. Usage of cannabis (lifetime consumption score) was correlated to increased volumes in certain subfields: the CA3 and CA4 in the right hemisphere and the presubiculum in both, the left and right hemispheres at baseline. Other tests including student’s t-test and multivariate analysis of covariance were performed. Tests to understand the effects of varying consumption were also performed. Persistent usage of cannabis, however, did not result in atrophy of the subfields over time. Rather, there were lower growth rates observed in the healthy controls group as compared to that of the cannabis users in certain subfields.

Yes! In general, we don’t see growth with use of medications, only shrinkage. I’ve only seen growth in articles with abstinence from alcohol. This combined with the article May show us a very different picture of THC than what we have been trained to see.