Cannabidiol Not Associated With Improvement in Chronic Schizophrenia

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oil dropper cannabidiol cannabis oil
No improvement in MCCB or PANSS scores were observed in patients who received augmentation with cannabidiol for schizophrenia.

A daily oral dose of cannabidiol 600 mg for 6 weeks did not produce improvements in cognition or disease symptoms for stable outpatients with chronic schizophrenia, according to a study published in Psychopharmacology.

The study sought to examine the effect of cannabidiol on cognitive impairments associated with schizophrenia and psychotic symptoms in chronically ill but stable patients with schizophrenia treated with antipsychotics. Data on cognition and symptoms were gathered using the MATRICS Consensus Cognitive Battery (MCCB) and the Positive and Negative Syndrome Scale (PANSS).

This randomized, placebo-controlled, double-blind, fixed-dose, parallel group trial lasted for 6 weeks, during which participants were given 600 mg of oral cannabidiol daily or a placebo. Forty-one individuals with schizophrenia were recruited for the trial and randomly assigned into groups, and 39 completed the study. There were 20 participants in the cannabidiol group and 19 in the placebo group. Cannabidiol treatment did not improve psychotic symptoms or improve cognitive impairments associated with schizophrenia in the study sample. These results conflict with the findings of some earlier case reports. Study investigators theorize that this could be because the 600 mg dose is lower than the 800 mg and 1000 mg doses used in earlier studies, and/or because the current study participants were stable, and in a later phase of illness.

Cognitive impairments associated with schizophrenia seem to be independent of treatment and phase of illness and are therefore thought to be a central feature of the illness. Contemporary antipsychotic drugs have little effect on cognitive impairments associated with schizophrenia, and block dopamine receptors. There is a need for effective cognitive impairments associated with schizophrenia treatments that target non-dopaminergic neurotransmitter systems.

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Study investigators conclude, “[while] adjunctive [cannabidiol] with antipsychotic treatment was well tolerated, it was not effective in treating [cognitive impairments associated with schizophrenia]. Future studies should assess if [cannabidiol] treatment earlier in the course of illness is beneficial. Finally, more studies should be conducted to determine an optimal oral dose of [cannabidiol] for treatment of symptoms and cognitive deficits in schizophrenia.”


Boggs DL, Surti T, Gupta A, et al. The effects of cannabidiol (CBD) on cognition and symptoms in outpatients with chronic schizophrenia a randomized placebo controlled trial [published online April 5, 2018]. Psychopharmacology. doi: 10.1007/s00213-018-4885-9