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Different Effects of Marijuana in Bipolar and Schizophrenic Patients

Different Effects of Marijuana in Bipolar and Schizophrenic PatientsCan using marijuana actually make you smarter?

A recent study suggests that some patients with bipolar disorder who use marijuana actually performed better on certain neurocognitive tests.   However, marijuana appeared to have the opposite effect on schizophrenic patients.

Dr. Ole Andreassen of Oslo University Hospital in Norway and his colleagues studied the effects of marijuana on bipolar and schizophrenic patients. They believe that the different effects of marijuana on cognition indicate “different underlying disease mechanisms in the two disorders.”

Marijuana is known to have a number of negative effects, including decreased cognition. Recent research has suggested that marijuana use can worsen symptoms of schizophrenia, and early use is associated with psychosis.  The effects of marijuana on bipolar patients are less well known. 

Andreassen and his team enrolled in their study 133 patients with bipolar disorder and 140 with schizophrenia.  The patients were questioned about prior drug use.  Over the previous 6 months, 18 bipolar patients and 23 schizophrenia patients had used marijuana.

All of the study participants then underwent several types of testing to assess neurocognitive function, including the logical memory test, the color-word interference set-shifting subset test, the digit span forward test, the verbal fluency test, and learning tests.

The bipolar patients who used cannabis performed better in verbal fluency than bipolar patients who did not use cannabis. They appeared to perform slightly better on the learning test, although these results were not statistically significant.

Marijuana use, however, worsened function in the schizophrenic participants, particularly with regard to focused attention, logical memory-learning, and logical memory-recall.

“Both neuropsychological test performance and individual effects of substance use can be regarded as endophenotypes, mediating factors between the neurobiological substrate and the expressed phenotype,” Andreassen writes.

Endophenotypes, characteristic traits used by researchers thought to be genetically linked to psychiatric disorders, are continually present even when more typical symptoms of mental illness are absent.   Some have postulated a biological relationship between bipolar illness and schizophrenia.  Andreassen’s results provide evidence to suggest that the two illnesses may be separate disease processes.

It is important to note that marijuana use results in a number of other negative effects that worsen overall function, and the data from this study do not promote the use of marijuana in bipolar patients.  Advises Andreassen, “The evidence linking drug use/abuse with poor outcome in severe mental disorder must still be decisive for clinical advice.”

Andreassen’s results are available in the November 2009 issue of Psychological Medicine.

Source:  Psychological Medicine

Different Effects of Marijuana in Bipolar and Schizophrenic Patients

Jessica Ward Jones, MD, MPH

APA Reference
Jones, J. (2018). Different Effects of Marijuana in Bipolar and Schizophrenic Patients. Psych Central. Retrieved on November 28, 2020, from
Scientifically Reviewed
Last updated: 8 Aug 2018 (Originally: 15 Jul 2010)
Last reviewed: By a member of our scientific advisory board on 8 Aug 2018
Published on Psych All rights reserved.