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Cannabis Abstinence May Improve Cognition in People with Depression, Study Suggests

By Alexander Beadle

Published: Jul 04, 2022   
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Four weeks of abstinence from cannabis may improve cognitive performance in people with major depressive disorder (MDD) and comorbid cannabis use disorder (CUD), a preliminary study has found.

Published in the American Journal on Addictions, the new work from researchers at the University of Toronto reports that visual search speed, sustained attention, and visuospatial working memory (VSWM) were all improved in participants following 28 days of abstinence from cannabis use.

Such cognitive improvements are important, the researchers say, as many treatments for MDD rely on patients having good cognition in order to properly engage with certain therapies, such as cognitive-behavioral therapy or mindfulness.

Abstinence may reverse some cognitive impairment

This preliminary study followed eleven patients diagnosed with MDD and CUD as they abstained from cannabis for 28 days. By the end of the study period, eight participants had been completely abstinent for the full length of time, with the remaining three reducing their cannabis use by more than 90 percent.

In addition to a two-hour-long battery of standard neurocognitive tests given at the initial session, participants were also asked to fill in a survey measuring psychiatric symptoms and to submit a urine toxicology test to verify their abstinence. The psychiatric survey and drug tests were re-administered weekly for the duration of the study, with the neurocognitive tests given again at the 14-day and 28-day marks.

The researchers found improvements in performance for all participants in tasks related to visual search speed, sustained attention, and VSWM by the end of the 28-day period. Increased performance in these domains was also determined to be independent of any improvements in depression, suggesting that cannabis abstinence was the main driver of these changes.

“Cognitive improvement occurred in tasks known to be mediated by the prefrontal cortex (PFC),” the researchers wrote. “In general, neuroimaging studies have observed greater and more widespread frontal activation in cannabis users than controls when completing VSWM and attention‐based tasks, which may suggest cannabis users must enhance activation of PFC to sustain behavioral performance.”

There were no significant differences in cognitive results between the complete abstainers and those who mostly reduced their use. However, the urine drug test data revealed that the three who did use cannabis most likely used it between the 7-day to 14-day mark and then maintained abstinence until the end of the study. As a result, their THC metabolite levels were broadly similar to the complete abstinence group.

No changes seen in memory after abstinence

Notably, this study found no significant changes in performance on either the immediate or delayed recall tasks after abstinence. This contrasts with other prior memory research conducted on healthy young adults, which found noticeable improvements in verbal learning and memory after four weeks of abstinence.

However, the researchers did note that the baseline scores for immediate recall were already close to normative levels, and so they say it is possible that “baseline ceiling effects” prevented any memory improvement from being detected in this study. Alternatively, with other studies of heavy cannabis users having still detected some memory impairment after over six months of abstinence, it could be that a longer-term abstinence study on individuals with MDD and CUD might turn up different results.

The researchers also note several other limitations on this preliminary study that could be improved in future works. For example, introducing a non-abstaining group and a group of healthy controls to compare results against could help to confirm whether these effects are indeed attributable to cannabis abstinence, and whether cognition is meaningfully impacted at baseline.

The small sample size here may have also limited the statistical power of the study, they say, and so a larger sample size could improve this while also increasing the generalizability of the findings to wider demographic groups.

Tackling CUD

Previous observational studies have found that young people with mood disorders and comorbid CUD are at a higher risk for self-harm. CUD itself is also associated with the development of anxiety and mood problems when a person is going through withdrawal. While the exact nature of the relationship between mood disorders, problematic cannabis use, and risks such as self-harm are unclear, identifying effective treatments for CUD has become a key area of research.

Perhaps counterintuitively, some of the most promising therapies for CUD are cannabinoid therapies. In a similar way to a person quitting cigarettes using a nicotine patch as a safer alternative, early trials have shown that the use of synthetic THC formulations can reduce withdrawal symptoms and relapse behavior in people with CUD.

Understandably, there are some concerns about giving THC formulations to youth and young adults who are struggling with problematic cannabis use issues. One recent study suggested that high doses of the non-intoxicating cannabinoid CBD may also help to promote continued abstinence in individuals with moderate CUD.

“We know that CBD has contrasting effects to THC on the endocannabinoid system,” study author Dr. Tom Freeman, told Analytical Cannabis following the study’s publication. “We know that THC is a partial agonist at cannabinoid receptors. But CBD has minimal direct activity at cannabinoid receptors.”

“At the same time, it does have properties that could be helpful in treating cannabis use disorder, such as inhibiting the effects of other ligands acting on the CB1 receptor and increasing endocannabinoids. And this is a potential mechanism through which it could be acting to alleviate the cannabis use disorder and help people cut down their use.”

This does not mean that people with CUD should begin self-medicating with commercial CBD products; the CBD capsules used in this study were an extremely pure formulation at doses exceeding what is normally seen on the commercial market. However, it does suggest that further research into CBD as a treatment for CUD may be warranted.


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