This exploratory study of 7 weeks was intended to be performed in 40 to 60 patients in up to 10 centers in Belgium. In a subset of patients, the 6-week treatment phase will be preceded by a single-dose cross-over phase with 1 week of wash-out. While the objective of the study, due to its exploratory design, is to assess any effect of the study medication on MRI or clinical outcome, the study medication is expected to improve the residual (remaining) positive symptom(s) of patients. In addition, genetic and pharmacokinetic testing may be performed to learn more about the disorder and its treatment.