Adding cannabis to cocaine use made cognitive problems worse, not better | Research

The takeaway

Cocaine users who also used cannabis heavily performed worse on processing speed, inhibitory control, and sustained attention compared to cocaine-only users, and cannabis did not reduce cocaine relapse rates over six months.

People interested in substance use treatment and the effects of polysubstance use on the brain.

Cannabis did not reduce cocaine relapse at any time point

What the researchers found

Both cocaine groups performed worse than controls on multiple cognitive measures. The cocaine + cannabis group performed worse than the cocaine-only group on processing speed, inhibitory control, and sustained attention, while the cocaine-only group did worse on mental flexibility. Cannabis use did not reduce cocaine relapse at 1, 3, or 6 months.

Why it matters

Some non-controlled studies have suggested smoked cannabis might help cocaine addiction. This study found the opposite: adding cannabis worsened cognitive outcomes without reducing relapse.

The numbers in context

63 cocaine + cannabis users, 24 cocaine-only users, 36 controls. Follow-up at 1, 3, and 6 months. Cannabis did not decrease relapse rates at any time point.

How the study worked

Compared 63 cocaine users with heavy cannabis use, 24 cocaine users with minimal cannabis use, and 36 controls. Neurocognitive testing occurred after two weeks of supervised detoxification, with relapse follow-up at 1, 3, and 6 months.

What this study cannot tell us

The cocaine + cannabis group was larger than the cocaine-only group, which may affect statistical power. Cannabis use was defined by a lifetime threshold (50 uses), not current frequency. This was not a randomized trial.

How to read the evidence

Moderate: prospective cohort with 6-month follow-up and appropriate control group, but not randomized.

When this study was published

Published in 2019.

The bigger picture

The idea of using one drug to treat addiction to another is appealing but risky. This study adds to the evidence that smoked cannabis is not a safe substitute therapy for cocaine dependence.

Questions still open

Would CBD alone (without THC) produce different cognitive or relapse outcomes? Does the timing and dose of cannabis use relative to cocaine use matter?

Common questions

Were people saying cannabis could treat cocaine addiction?

Some non-controlled studies and anecdotal reports suggested smoked cannabis might help cocaine users reduce use. This study tested that claim with cognitive and relapse data and did not find support.

Did cannabis help with any aspect of cocaine recovery?

The cocaine + cannabis group performed better on mental flexibility, but worse on three other cognitive measures, and cannabis did not reduce relapse rates.

Read the original research

Distinct effects of cocaine and cocaine + cannabis on neurocognitive functioning and abstinence: A six-month follow-up study.

Drug and alcohol dependence, 205, 107642

View on PubMed ↗Publisher’s paper ↗

Citation

Oliveira, Hercílio Pereira de; Gonçalves, Priscila Dib; Ometto, Mariella; Santos, Bernardo Dos; Malbergier, André; Amaral, Ricardo; Nicastri, Sergio; Andrade, Arthur Guerra de; Cunha, Paulo Jannuzzi. (2019). Distinct effects of cocaine and cocaine + cannabis on neurocognitive functioning and abstinence: A six-month follow-up study.. Drug and alcohol dependence, 205, 107642. https://doi.org/10.1016/j.drugalcdep.2019.107642