Dr. Hennessy conducts research in the field of pharmacoepidemiology, which is the study of the health effects of drugs and other medical products in populations. His team has identified a survival benefit of potassium supplementation in users of loop diuretics and studied serious health consequences of drug-drug interactions involving high-risk drugs including anticoagulants, antidiabetes agents and antiplatelet agents. His research has produced crucial knowledge about the cardiovascular safety of many widely-used drugs for mental health conditions including ADHD, depression and schizophrenia. He also evaluated an early approach to using medical insurance data to improve prescribing, finding it ineffective despite its federal mandate. This contributed to the omission of drug utilization review programs from Medicare Part D.He co-led a pair of studies demonstrating the effectiveness and safety of the SA14-14-2 vaccine for Japanese encephalitis (JE), which subsequently led to the immunization of millions of children per year in many populous countries, including Cambodia, India, Malaysia, Nepal, Sri Lanka and Thailand. Use of that vaccine has been credited with reducing the incidence of JE. He co-developed the trend-in-trend research design for study of the effects of rapidly increasing or declining exposures. For  example, the approach could be used to examine whether heart attack risk is increased among subgroups who adopt a new drug at a faster rate. He was also the senior author of a citizen petition to the U.S. Food and Drug Administration that led to re-labeling of metformin, the best-proven oral drug for diabetes, to permit its use in persons with mild to moderate renal insufficiency. 

Dr. Hennessy is a past scientific chair and past president of the International Society for Pharmacoepidemiology, and has served on the FDA’s Drug Safety and Risk Management Advisory Committee and the board of directors of the American Society for Clinical Pharmacology and Therapeutics. He is a co-editor of the books Pharmacoepidemiology, 6th edition and Textbook of Pharmacoepidemiology, 2nd edition.

Other Positions:

Interim Director, Division of Epidemiology, DBEI

Director, Center for Pharmacoepidemiology Research & Training

Chair, Health Services Quality and Effectiveness Study Section, US National Institutes of Health
Senior fellow, Leonard Davis Institute of Health Economics
Fellow, Institute on Aging
Member, University of Pennsylvania Health System Pharmacy & Therapeutics Committee

Courses Led: 
EPI 666: Pharmacoepidemiology Research Methods

Honors:
1998 Stanley A. Edlavitch Award for Best Abstract Submitted by a Student, International Society for Pharmacoepidemiology
2002 Saul Winegrad Award for Outstanding Dissertation in Epidemiology and Biostatistics, University of Pennsylvania
2005 Young Alumnus Award, University of the Sciences in Philadelphia
2008 Leon I Goldberg Young Investigator Award, American Society for Clinical Pharmacology & Therapeutics
2013 Samuel Martin Health Evaluation Sciences Research Award, University of Pennsylvania Perelman School of Medicine
2014 Julius W. Sturmer Memorial Lecture Award, Alpha Tau Chapter of the Rho Chi Society, Philadelphia College of Pharmacy, University of the Sciences
2015 Elected Member, National Academy of Medicine