Dr. Siegel is the director of the Internal Medicine and Primary Care Clinic at McLean Hospital and the MGH Internal Medicine Associates, Belmont, Massachusetts. He is an associate professor of medicine at Harvard Medical School and a fellow of the American College of Physicians. Clinical expertise includes substance dependency, eating disorders, transgender and sports medicine. He is the author of more than 50 original research papers on diverse subjects from medical complications of cocaine usage to the evaluation and management of hyponatremia in psychiatric patients.

As a former marathoner, his research on runners in Boston has contributed to the prevention and emergent treatment of life-threatening, if rare, complications, including cerebral edema from water intoxication in young females, and cardiac arrest in middle-aged males, respectively. His advocacy for use of pre-race aspirin to prevent cardiac events in susceptible runners is presented in Harvard Medicine, winter/spring 2014.