Cannabis use may attenuate neurocognitive performance deficits resulting from methamphetamine use disorder

Methamphetamine use is widely associated with significant neurocognitive deficits, including impairments in memory, executive function, and processing speed. Because a large portion of methamphetamine users also use cannabis, the researchers sought to understand if co-occurring cannabis use influences these cognitive outcomes. Using a sample of 423 participants, they stratified individuals into four groups based on their lifetime diagnoses of methamphetamine (M) and cannabis (C) use disorders: M+C+, M-C+, M+C-, and M-C-. The study utilized comprehensive neuropsychological assessments to calculate global and domain-specific neurocognitive scores, while controlling for potential confounders such as current depressive symptoms, hepatitis C status, and other lifetime substance use.

The study found that individuals who met the criteria for both methamphetamine and cannabis use disorders (M+C+) performed significantly better than those who used only methamphetamine (M+C-). This pattern was consistent across several domains, including verbal fluency, information processing speed, learning, and memory. Furthermore, the M+C+ group showed a lower likelihood of global cognitive impairment compared to the M+C- group. Interestingly, the M-C+ group performed similarly to the M-C- control group, suggesting that a lifetime cannabis use disorder does not exacerbate, and may even be associated with better performance in specific areas compared to individuals without any substance use disorder.

These findings challenge the notion that co-occurring cannabis use uniformly exacerbates substance-induced cognitive decline. Instead, they suggest that cannabis use might have neuroprotective properties that attenuate some of the neurological damage associated with methamphetamine use. Given the high rates of co-use, this study highlights the need for further longitudinal research into the potential role of cannabinoids in mitigating methamphetamine neurotoxicity.