Poorer neurocognition in young psychosis patients with current cannabis use

Adult psychosis patients (i.e. over the age of 25 years) who are also lifetime cannabis users (CANN+/-) appear to exhibit superior cognition compared to never-using patients (CANN-). The objective of this meta-analysis was to evaluate the cognitive differences between CANN- and patients who currently use cannabis (CANN+) (i.e. during the CANN ± patients’ cannabis-using stage). Specifically, focusing on young patients under the age of 25 years, the typical stage of both psychosis- and cannabis-onset.

Of the 308 studies identified through database searches and secondary referencing, 14 compared neurocognition of CANN+ and CANN- in young people with psychotic disorders (mean age between 15 and 45 years). Effect sizes were extracted using neurocognitive test performance between CANN+ and CANN- and random effects modelling was conducted on pooled ES and moderator analyses.

CANN + performed worse on several cognitive domains (i.e. premorbid IQ, current IQ, verbal learning, verbal working memory, motor inhibition) compared to CANN-. The association between age and performance in CANN + cognition was varied, with older age predictive of worse performance in processing speed, sustained attention, verbal memory, and better performance in verbal learning and very fluency. Of note, CANN + outperformed CANN- in tests of conceptual set-shifting.


These results are consistent with previous findings indicating that CANN + (users of cannabis) demonstrate poorer neurocognition than CANN-; and that this is exacerbated with increasing age. Our findings demonstrate significant cognitive differences between patients with CANN + versus CANN- even at early-onset psychosis, which could suggest a different underlying mechanism towards psychosis for cannabis users.

Young people, Schizophrenia, Early-onset psychosis, Cognition, Marijuana, Comorbidity


It states at the beginning:

and then goes on to state evidence that proves the case is not true:

The only thing cannabis users were reported to have been better at were:

Then it goes on to say:

Thus this seems to be a hatchet job of epic biased proportions where it begins by saying it is better for superior cognition, but uses its findings to prove otherwise.

So, is it better or not? because it seems this study has tried to prove otherwise.

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I think they are saying overall CANN+ demonstrate poorer cognition rather than demonstrating poorer cognition in all domains.

To give an example: 6 domains-1,2,3,4,5,6, A outperforms B in 1,2,4 and 6 . B outperforms A in 3 and 5.

yet they start out by saying “superior cognition”. Which would imply that overall it is better. It didn’t state it was better in some areas and worse in others. It stated superior which dictionary definition means of a higher standard or quality.

I think you are splitting hairs. " Superior cognition" doesn’t have to mean better in all areas. It just means that overall cognition is better.

So in this report it contrasts 1 positive (outperformed in set shifting) against 5 negatives (premorbid IQ, current IQ, verbal learning, verbal working memory, motor inhibition) in testing, yet still believes it to be superior. Biased reporting or what?

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Any mind altering substance, in theory, can help someone recall a time or place or any information given that they were under the same mind altering substance in the time that they want to recall from. That’s why students take speed for the college tests. That’s how PTSD works and why it’s labeled as a disorder. However there are significant superior ways to recall information that don’t require taking a drug and that will be more lenient on your mind.

I’m failing to see any bias. All they have done is report where CANN- outperforms CANN+ and vice versa.

Maybe the nuance is in the first sentence.

Perhaps that was their premise for doing the experiment and the results were contrary to that and consistent with what they found before in earlier studies.

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It would appear that cannabis has a greater negative effect on cognition at a younger age. The thing would be test those who start cannabis at 25- and those who start cannabis at 25+.

Cannabis with constituents of thc and other thcv etc. might not help in most cognition, but studies have proved that cbd alone can help cognition for sz users:

"Researchers at the Illawarra Health and Medical Research Institute conducted an animal study to investigate the non-psychoactive cannabinoid’s ability to alleviate cognitive impairment and improve learning, memory and attention in patients with schizophrenia.
“We found that CBD was able to restore recognition and working memory, as well as social behavior to normal levels,” said PhD candidate and researcher Ashleigh Osborne. “These findings are interesting because they suggest that CBD may be able to treat some of the symptoms of schizophrenia that are seemingly resistant to existing medications.”

It’s comparing over 25 age users vs under age 25 users.

Probably not all that odd, since there have been other studies showing greater negative effects for use starting at a young age.