Acute Effects of Cannabis on Cognition and Mobility in Older HIV-infected and Uninfected Women

Cannabis is the most prevalent drug used by adults aged 50 and older in the U.S., after alcohol and tobacco. Recent trends show dramatic increases in cannabis use among older U.S. adults, and rising cannabis tetrahydrocannabinol (THC) content. Cannabis intoxication acutely alters short-term memory, attention span, verbal fluency, reaction time, and psychomotor control. Heavy long term cannabis use has been associated with lasting impairments in verbal learning, memory, and attention that correlate with duration of use; however, other studies have found that cognitive deficits from cannabis are reversible and related to recent exposure. But studies on cannabis exposure and cognition are age limited by including only adolescents through middle-aged adults; effects of acute and long-term cannabis use on cognition among older adults are virtually unknown. Given the rising potency and increasing frequency of cannabis use among older adults, studies systematically examining the risks and benefits of cannabis use in older adults are urgently needed.

Cannabis use is particularly common in people living with HIV (PLWH), with 12- 56% prevalence rates compared to 9.5% in the general U.S. population. HIV has detrimental effects on both mobility and cognition, and similar to normal aging, mobility in patients with HIV may be influenced by cognitive function. Mild-to-moderate neurocognitive impairments (NCI), notably in attention and executive functions, remain highly prevalent and persist despite suppressive antiretroviral therapy, affecting almost half of PLWH. Little is known about the combined effects of cannabis use and HIV infection on cognition and mobility, particularly among older individuals. As the population of older PLWH continues to grow, co-occurring aging and HIV related declines in cognition and mobility will coincide; the effects of continued cannabis use In the Women's Interagency HIV Study (WIHS), it was found that current cannabis use was associated with over double the odds of single fall, and over 2.5 times the odds of multiple falls in 6 months; past cannabis use was associated with over 1.5 greater odds of single fall and multiple falls. Preliminary data shows that 40% of WIHS women (mean age 48) reported at least one fall over 2 years; current cannabis users had 1.7 times greater fall risk among HIV+ but not HIV-women. The hypothesis is that falls are related to acute effects of cannabis on attention and mobility, and that given subtle, pre-existing deficits associated with HIV infection, these acute cannabis effects may be more pronounced in HIV+ women, placing them at increased risks of falls. Whether this observed fall risk associated with cannabis use represents acute effects, or persistent effects of past cannabis use on cognition, balance, or mobility, or whether adverse effects of cannabis differ by HIV status merits further study in this aging population.

The "Walking While Talking" (WWT) test requires individuals to walk while performing a secondary attention-demanding task (dual task), has been used to assess the interactions between cognition and gait, and provides a framework for evaluating the effect of divided attention, a facet of executive functions, on mobility. Increased dual task costs measured using WWT may help unmask subtle and latent cognitive abnormalities before they become clinically apparent by increasing the complexity of the walking condition, and predict falls, frailty, disability, and mortality among older community-residing adults. Because both cannabis use and HIV have been implicated in impairments in attention and executive functions, the WWT may be a quick and simple mobility stress test to identify subtle cognitive and motor effects of acute cannabis administration as a function of HIV status.

The objective is to explore the mechanisms that underlie the increased fall risk associated with cannabis use. The effects of controlled administration of active (7.0% THC) and inactive (0.0%) cannabis in aging HIV+ women on stable HAART and HIV- controls enrolled on the WIHS will be compared. Endpoints will be balance, mobility, and cognition, including a cognitive-motor divided attention task (WWT). Specific aims and hypotheses are:

1. To determine the acute effects of cannabis on balance and mobility among older HIV+ and HIV- women. These test will be performed within subject comparisons of performance on balance and mobility tests at two supervised visits, with administration of placebo vs. active cannabis in counter-balanced order. The hypothesis is that HIV+ women will have greater impairment on balance and mobility, especially on complex walking conditions that demand attention, with administration of active cannabis than HIV- women
2. To determine the acute effects of cannabis on cognition among older HIV+ and HIV- women.HIV+ women will have greater impairment on cognitive testing, especially in attention, with administration of active cannabis than HIV- women.