A team of researchers at the University of California, San Diego, published findings indicating that daily cannabis use led to lower neuroinflammation in cerebrospinal fluid (CSF) but not plasma – these are parts of the lower central nervous system – in a sample group of people with human immunodeficiency virus (HIV). 
The study’s findings, especially if confirmed by other research groups, signifies that medicinal cannabis can be used by people with HIV to reduce chronic inflammation and negative cognitive impacts of HIV, mainly, in the realm of learning. Recent work from the group had found that verbal fluency improved with cannabis use. 
The researchers had been well aware of other studies that had found cannabis use to be linked with lower rates of neurocognitive impairment in HIV-positive individuals, and posited that the anti-neuroinflammatory properties of the plant had a role in this.
The Study’s Hypothesis
The team hypothesized that lower levels of pro-inflammatory biomarkers linked with cannabis use would lead to better performance in some cognitive domains among the HIV-positive individuals, such as in learning and verbal fluency.
The study researched the effects of three kinds of cannabis use – no cannabis use (105 individuals), moderate cannabis use (62 individuals), and daily cannabis use (31 individuals) – on cerebrospinal fluid and plasma inflammatory biomarkers of the three groups of HIV-positive individuals. A non-cannabis-using group of HIV-negative people (65 individuals) were used as a control. Also, it should be noted that 75% of daily cannabis consumers reported using less than 1.1 grams of cannabis per day.
How the Study was Undertaken
First, the study authors evaluated cognitive performance by cannabis use group before launching the study; then, second, they assessed inflammatory biomarker levels during the cannabis use period of six months. Third, they took note of cognitive performance in seven domains during these same six months, including learning and verbal fluency, as previously mentioned, as well as executive function, processing speed, attention/working memory, delayed recall/memory, and motor skills.
The researchers were careful to study whether there were direct links between cannabis recency, quantity, or frequency, with the CSF and plasma biomarkers of the HIV-positive people.
Two CSF inflammatory biomarkers – MCP-1 (macrophage inflammatory protein) and IP-10 (interferon-gamma-inducible protein-10)– were lower in HIV-positive daily cannabis users compared to HIV-positive non-cannabis users. CSF IP-10 was higher in HIV-positive moderate and non-cannabis users in comparison to the HIV-negative non-cannabis users.
Plasma inflammatory biomarkers, in turn, did not change during the study across the groups. Plasma IP-10 levels remained elevated in all three HIV-positive groups.
Study findings backed the researching team’s hypotheses that frequent cannabis use can reduce neuroinflammation in HIV-positive people, with potential benefits for cognition. The latter consisted of the group of daily cannabis-using HIV-positive individuals performing higher scores in global cognition and a number of cognitive domains, such as learning, compared to HIV-positive moderate users and HIV-positive non-cannabis users.
The researchers credited the better cognitive performance of the daily cannabis-user group to lower CSF levels of MCP-1 and IP-10. The team further found that greater total days of cannabis use, considerably predicted lower levels of MCP-1 and IP-10 biomarkers; when cannabis recency and cannabis quantity did not. Frequent, but not heavy cannabis use characterized the daily cannabis group – 75% of daily users used less than 1.1 grams of cannabis a day.
References: Watson CW, Campbell LM, Sun-Suslow N, et al. Daily cannabis use is associated with lower CNS inflammation in people with HIV. J Int Neuropsychol Soc. 2021;27(6):661-672. [journal impact factor = 2.892; times cited = 1]
 Watson CW, Paolillo EW, Morgan EE, et al. Cannabis exposure is associated with a lower likelihood of neurocognitive impairment in people living with HIV. J Acquir Immune Defic Syndr. 2020;83(1):56-64. [journal impact factor = 3.475; times cited = 18]