Patients' beliefs about medicine are associated with early thiopurine discontinuation in patients with inflammatory bowel diseases.

"Conflicts of interest There are no conflicts of interest."

"The TOPIC trial was funded by The Netherlands Organisation for Health Research and Development (grant number 94507606) and the participating institutes."

"The current study is a post-hoc analysis of the Thiopurine response Optimization by Pharmacogenetic testing in Inflammatory bowel disease Clinics (TOPIC) trial. In the TOPIC trial, thiopurine-naive patients with IBD were randomized for standard-of-care thiopurine dosing versus a genotype-based dose to evaluate the efficacy of pretreatment thiopurine S-methyltransferase genotyping on the occurrence of myelosuppression . Patients were followed for 20±6 weeks. Physicians were free to use either azathioprine or mercaptopurine. The main exclusion criteria were previous use of thiopurines, laboratory test abnormalities, known thiopurine S-methyltransferase enzyme activity, or genotype. The study protocol of the TOPIC trial was approved by the Institutional review board of the Radboud University Medical Center. All patients provided written informed consent. The TOPIC trial was registered at clinicaltrials.gov, NCT00521950. The TOPIC trial complies with the Declaration of Helsinki. For a detailed description of the study design, patient selection, and patient data, we refer to Coenen et al. ."