This article is more than 5 years old. Information may no longer be current.

Effects of cannabis use on psychosis may vary depending on frequency, potency

Continued use of highly potent cannabis in the first 2 years after onset of psychosis led to poorer outcomes, including increased risk for subsequent relapse and shorter time to relapse, according to recent findings.

“Whether the association between cannabis use and worse outcome in pre-existing psychosis is causal has remained inconclusive because prospective evidence so far has not always established that cannabis use actually preceded and was in reasonable temporal proximity to the outcome of interest (ie, relapse of psychosis),” Tabea Schoeler, MSc, a research student at King’s College London, and colleagues wrote. “More importantly, how parameters of cannabis use, such as type and potency of cannabis used and frequency of use, affect outcome has remained unclear. This gap in the scientific literature is especially important in view of findings that dose, type, and pattern of cannabis use are important determinants of its effect on onset of psychosis.”

To assess effects of continuation, frequency and type of cannabis on relapse in the first 2 years after psychosis onset, researchers evaluated 256 individuals aged 18 to 65 years who presented with their first episode of psychosis to psychiatric services between April 2002 and July 2013. Participants were followed until September 2015.

Former regular users of cannabis who stopped after psychosis onset had the best relapse outcomes, according to researchers.

Continued high-frequency users of highly potent cannabis had the worst outcomes, with an increased risk for subsequent relapse (OR = 3.28; 95% CI, 1.22-9.18), more relapses (IRR = 1.77; 95% CI, 0.96-3.25), shorter time to relapse and more intense psychiatric care (OR = 3.16; 95% CI, 1.26-8.09) after onset of psychosis.

“Findings presented by Schoeler and colleagues support the idea that clinicians should actively intervene and help patients to quit cannabis and remain abstinent,” Rachel A. Rabin, BSc, MSc, PhD, and Tony P. George, BSc, MD, of the Centre for Addiction and Mental Health (CAMH), Toronto, wrote in an accompanying editorial. “Nevertheless, the investigators suggest a possible harm reduction model in which interventions could focus on persuading cannabis users to reduce use or shift to less potent forms of cannabis, especially patients with psychosis who are otherwise unable to stop using cannabis. However, the proposal of such a framework might be problematic.” – by Amanda Oldt

Disclosure: Schoeler reports no relevant financial disclosures. Rabin reports no relevant financial disclosures. Please see the full study for a list of all authors’ relevant financial disclosures.