The research of Prof van Schaik focusses on the clinical implementation of DNA analysis to guide drug therapy. Research topics include Solid Organ Transplantation, Oncology, Pain and Psychiatry, as well as the use of cell free DNA as a biomarker in oncology and solid organ transplant rejection. Additional lines of research are Cardiac Markers and Prostate Cancer. Prof van Schaik has published >290 articles (h-index 63) and has given >500 invited lectures at national and international conferences. He participates in several national and international committees on pharmacogenetics.