Cannabis use may be associated with less HIV-related cognitive impairment, suggests new research from Caitlin Wei-Ming Watson and colleagues at the University of California, San Diego. The study, which included about 1,000 adults with varying histories of cannabis use, found lower rates of difficulties with learning and verbal fluency in people living with HIV who used cannabis.
There were no differences in cognitive impairment between HIV-negative cannabis users and non-users, which suggests that cannabis may prevent neurocognitive impairment from HIV.
“Recent research shows that cannabinoids have anti-inflammatory properties,” said Watson. “We hypothesized that some degree of cannabis exposure may be protective for brain health in certain contexts. While in the general population, heavy cannabis use is associated with null or negative cognitive outcomes, we were interested in whether cannabis would show different effects on cognition in a disease like HIV, which is characterized by a weakened immune system and persistent inflammation.”
A total of 952 adults participated in the study (679 who were living with HIV, 273 who were HIV-negative). People with a history of non-HIV-related neurological, medical or psychiatric disorders affecting brain function were not included in the study. People with a substance use disorder (other than cannabis) in the past year, and people who tested positive for substances other than cannabis on a urine toxicology screen were also not included in the study.
The researchers assessed lifetime cannabis use and cannabis use in the previous year, categorizing study participants based on HIV status and cannabis exposure. People in the cannabis group had both a history of substantial cannabis use and cannabis use in the previous year. People in the cannabis-negative group did not use cannabis in the previous year and did not have a history of substantial use. Participants completed neurocognitive tests to assess cognitive functions including verbal fluency, learning, memory, attention, motor skills and more.
Participants ranged in age from 18 to 79 years. Most were men (76%) and identified as gay or bisexual (71%).
After controlling for race/ethnicity, current major depressive disorder and history of substantial methamphetamine use, the researchers found a significant relationship between cannabis use and neurocognitive impairment that varied by HIV status.
Rates of neurocognitive impairment among HIV-negative people were similar regardless of cannabis exposure (between 25% and 30%). However, among people living with HIV, rates of neurocognitive impairment were much higher among non-cannabis users (nearly 50%), while rates were much lower among cannabis users (about 30%).
“Our results are consistent with the idea that under some circumstances, cannabis might be neuroprotective,” the authors said. “Given our findings did not differ in virally suppressed people living with HIV, the anti-inflammatory effects of cannabis may be important for people living with HIV who are both detectable and undetectable.”
Watson explained that the majority (70%) of neurocognitive deficits observed in people living with HIV are considered mild enough that people may not notice impairment, although even these milder forms of neurocognitive impairment may influence everyday life.
“Some research from our lab has shown that these mild impairments are linked to difficulties with medication management, employment, and other important functional and medical outcomes,” she said.
Further research is needed to clarify what aspects of cannabis are therapeutic or not therapeutic—including the effect of dose, frequency of use and type of cannabis product. Watson stated that their findings have several limitations.
“Our study was retrospective and did not capture detailed information about cannabis use such as potency, nor did we capture important factors such as psychosocial context, including motivations for cannabis use. There also may be other negative health consequences of heavy long-term cannabis smoking such as chronic bronchitis which are important to keep in mind.”
“In the future, we would like to be able to define what levels of cannabis exposure are linked to optimal brain and cognitive health, and what levels may be detrimental,” said Watson. “It is likely that beneficial effects are limited to certain dose and frequencies of use, and also vary by cannabis compound (e.g., THC vs. CBD vs. CBC).” At this point, we don’t want the take-away to be, ‘If you have HIV, you can use cannabis and that’s going to be really good for your brain health and cognition.’ We need to do much more research before we can make more specific recommendations regarding the impact of cannabis use on the brain in HIV disease.”
Watson, Caitlin Wei-Ming, and colleagues. Cannabis exposure is associated with a lower likelihood of neurocognitive impairment in people living with HIV. JAIDS, January 2020.
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