At Dalhousie University in Halifax, Canada, Dr. Tan was Professor of Medicine and Biochemistry as well as Head, Division of Endocrinology and Metabolism in the Department of Medicine. There, he was active in clinical practice, research, education, and administration. Next, at Eli Lilly and Company, Indianapolis, he was Distinguished Medical Fellow at Lilly Research Laboratory and Global Medical Director for Diabetes. He then joined University of Michigan in Ann Arbor as Professor of Internal Medicine in the Division of Metabolism, Endocrinology & Diabetes. He is currently Professor Emeritus (Active) there.