Posted on: November 22, 2016 at 3:17 pm
Last updated: September 26, 2017 at 7:21 pm

This article was reposted with permission from our friends at

Finally, a study to break the stigma that cannabis makes people dumb. This is probably what a lot of people thought when they heard of this long-term study on marijuana’s long-term effects on the brain. While taking this drug can definitely make some people lazy, unproductive, and your your fridge clean, mounting evidence suggests that cannabis does not harm your brain.

A study from Massachussetts’ McLean Hospital has discovered that the herb can, in fact, improve cognitive functioning over time. The study, which will continue for at least two years, is headed by Staci Gruber Ph.D. who heads the Marijuana Investigations for Neuroscientific Discovery (MIND). It is the first of its kind to measure the impact of medical cannabis on cognitive performance by measuring the participants’ cognitive performance in 3, 6, and 12-month intervals.

Gruber’s Cannabis Study Findings

cannabis plant

“After three months of medical marijuana treatment, patients performed better, regarding their ability to perform certain cognitive tasks, specifically those mediated by the frontal cortex,” according to Gruber.

The participants also reported improvements in many other areas such as better sleep, developments in specific ailments, and overall health. They also stated that ongoing cannabis use has led to a reduction in dependency on conventional but synthetic and harmful medicines.

There was also a 42% reduction in opiate usage among participants. “This is significant, particularly for those of us in Massachusetts and other areas of the country where the opioid epidemic is ravaging so many,” Gruber added. “[The results so far] certainly warrant deeper and broader investigation.”

As in any study, some factors exist that may have affected the findings, some of which include the participants’ age, differences in the chemical makeup of various cannabis products, and how they use those products. Most of them are designed to be low in THC which is responsible for getting you “high,” while they contain a large amount of other cannabinoids like CBD which may offset some of the side effects of THC.

Marijuana Effects on the Brain

Recreational cannabis is well-loved for its high THC content. However, the study analyzes the effects of different medical cannabis products that were used by the patients. Through this long-term study, Gruber hopes to establish a better understanding of the role that various cannabinoids play over months or years of use and how combining them can affect brain function in the long-run.

Over the course of the study, Gruber hopes to learn more about the impact of these chemical differences. While the preliminary results have been released and published in Frontiers in Pharmacology, the study will continue to monitor the patients and even have them undergo a multimodal neuroimaging component. The test will help the researchers identify the impact, if any, of cannabis on human brain’s structure and how this will, in turn, affect mood and cognition over time. If the positive evidence that Gruber has collected so far continues over the next two or more years, maybe the general public will embrace the true and helpful effects of cannabis on our brains and well-being.

“As a clinical researcher, I’m not interested in exploring only the good or the bad, I’m only interested in the truth,” says Gruber. “That’s what our patients and our recreational users have a right to know and a right to expect from us. People are going to use it. It’s up to us to figure out the very best and safest ways in which they can do that.”

As of the time of writing, there have been 32 patients who have finalized screening procedures. Out of these, 24 medical cannabis users have already been enrolled in the study.


To participate in the study, the participants are required to be naïve about the drug. But if they have had a history of using medical cannabis they should have abstained for at least ten years to make sure that recent exposure to the herb doesn’t affect the results. Urinalysis was used to confirm the reports of patients who had previously used it.

Past studies have suggested that using the drug can harm the brain, especially if employed by those who are still growing. McLean Hospital’s study, however, has proven to be a pivotal first step in analyzing the true long-term effects of cannabis on the brain and cognitive functioning.

Other Studies On Cannabis and The Brain

Gruber’s study isn’t the first to shed light on the long-term effects that cannabis has on the brain.

In the past, there have been other studies which have yielded positive results on how cannabis affects brain function over both short and longer periods of time. A 2013 study conducted by researchers at the University of Minnesota and published in the Journal of Clinical and Neuropsychology discovered that college students who used cannabis scored better in their exams which tested verbal fluency and processing speed. However, researchers were surprised because “marijuana use during this age span has been most strongly associated with cognitive impairment.”


In a 2001 study led by Dr. Carl Heart of the New York State Psychiatric Institute, researchers analyzed the effects of both low and high doses of THC in chronic users. The results showed that neither kind of dosage impaired the attention of participants when compared to a placebo trial. In fact, participants who were exposed to high doses of THC showed significantly better performance in a task that required them to engage in visual tracking activities.

Short Answer: No, Cannabis Doesn’t Equate to Lack of Intelligence

While it may affect individuals in a way that some people perceive as negatively, fairly big studies as well as more and more lengthier ones consistently see more positive takeaways than negative ones. Hopefully, with further future exploration, we’ll be able to better identify any flaws in past research studies and evaluate with greater accuracy how cannabis will continue to affect the human brain with continued use, and the role that dosage plays.


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