Chronic Marijuana Use Unlikely to Further Harm the Brain in HIV

By Marilynn Larkin

August 27, 2020

NEW YORK (Reuters Health) - HIV-positive individuals who regularly use marijuana likely face no additional brain inflammation or cognitive deficits, researchers say.

"We found the typical ongoing brain inflammation in many brain regions, and some cognitive deficits in attention and memory" associated with HIV infection, Dr. Linda Chang of the University of Maryland School of Medicine in Baltimore told Reuters Health by email. But patients who used marijuana regularly at least three times a week for close to 20 years "showed no additional brain inflammation, as measured by diffusion tensor imaging and multiple brain regions, (and) did not show additional cognitive deficits."

"They showed abnormality in only one of the white matter tracts that is connected to brain regions rich in cannabinoid receptors, which binds to THC, the major active ingredient of marijuana," she said. "However, the abnormal diffusion in the white matter tract in the marijuana users suggests axonal loss in this tract, which connects to brain regions involved in verbal memory and emotion."

As reported in the Journal of Neuroinflammation, Dr. Chang and colleagues studied 44 HIV+ individuals (23 minimal/no marijuana users, 21 chronic users) and 46 seronegative participants (24 minimal/no users, 22 users). Overall, the mean age was about 45 and about 90% were men. Other demographics and baseline characteristics were similar among the groups.

Chronic marijuana use was defined as more than three times/week for more than two years and negative screens for other drugs of abuse.

Groups were compared on tests of seven domains of neuropsychological performance, as well as on diffusion tensor imaging metrics, using an automated atlas to assess fractional anisotropy (FA), axial (AD), radial, and mean diffusivities (MD), in 18 cortical and four subcortical brain regions.

Compared to seronegative participants and regardless of marijuana use, the HIV+ group had lower FA and higher diffusivities in multiple white matter and subcortical structures, as well as poorer cognition in fluency, attention/working memory, learning, and memory.

Regardless of HIV serostatus, marijuana users had lower AD in the uncinate fasciculus, but similar cognition as nonusers.

As Dr. Chang noted, HIV serostatus and marijuana use showed an interactive effect on MD in the right globus pallidus, but not on cognitive function. Lower FA in the left anterior internal capsule predicted poorer fluency across all participants and worse attention/working memory in all except minimal users; higher diffusivities in several white matter tracts also predicted lower cognitive domain Z-scores.

Marijuana users - regardless of HIV serostatus - showed greater than normal age-dependent FA declines in the superior longitudinal fasciculus, external capsule, and globus pallidus, suggesting that "older chronic (marijuana) users may eventually have lesser neuronal integrity in these brain regions," the authors note.

Dr. Joshua Barocas, an infectious diseases physician at Boston Medical Center, commented by email, "The study confirmed what we know, which is that HIV is alone is associated with cognitive impairment. As many patients and clinicians are adopting a harm-reduction model of care, this study provides some support that if, for example, an adult patient is most concerned about future cognitive impairment, marijuana may not be as problematic as other substances."

"While compelling," he added, "I would not generalize these data to adolescents or younger adults as there is probably some harm to chronic marijuana use in younger populations."

April Hatch, a registered nurse and founder of the Cannabis Care Team in Lees Summit, Missouri, also commented in an email to Reuters Health. "Unfortunately, with this study and many like it, they categorize subjects as cannabis users or non-users, and this limits what we can truly know about how cannabis consumption affects us and our brain. A patient taking 5 mg of an edible each night for sleep gets lumped into the same category as someone who uses highly potent concentrates daily. These two patients are likely to have very different effects, yet are in the same group."

SOURCE: Journal of Neuroinflammation, online August 6, 2020.