In this project, we propose to study endocannabinoid control of microglia activation as a new therapeutic target in the treatment of schizophrenia. Using a placebo-controlled, randomised, double-blind design, we will investigate this in a group of 50 recent-onset schizophrenia patients after four weeks of daily CBD treatment, in addition to their regular antipsychotic medication. First, we will examine if CBD treatment attenuates microglia activation and levels of peripheral inflammatory markers. In vivo microglia activation is assessed before and after treatment using Positron Emission Tomography (PET) in combination with the tracer [11C]-R-PK11195. Second, we will determine if reduced microglia activation and levels of inflammatory markers relate to improvement of symptomatology and cognitive function. Third, we will assess how microglia activation and levels of inflammatory markers before treatment predict the clinical response to CBD.