Cannabidiol (CBD) is disclosed for use as an adjunct medicament in the treatment of mental disorders where psychotic symptoms are being treated with a typical or an atypical antipsychotic, wherein the CBD is for use to augment the effect of the antipsychotic medicament. The antipsychotic may be olanzapine or quetiapine. Also disclosed are compositions comprising CBD in combination with one or more antipsychotics such as olanzapine and quetiapine. In particular the adjunct therapy relates to the treatment of schizophrenia or related psychotic disorders, more particularly those which are considered to be treatment resistant. The adjunct therapy may also be used to treat positive and/or negative symptoms in mental orders such as schizophrenia, i.e., anhedonia, asociality, avolition, apathy, attention disturbance or cognitive symptoms such as working memory, motor speed and executive function. CBD may also be used as a monotherapy to treat said positive/negative symptoms.
