Professor O’Mahony graduated MB BCh BAO with honours in 1985. His early clinical training was at Cork University Hospital (CUH) where he completed basic professional training and obtained membership of the Royal College of Physicians of Ireland in 1987. After one year as a registrar trainee and completing basic professional training in CUH, he moved to a research fellowship post in St. James’s Hospital, Dublin, under the supervision of the late Prof. Davis Coakley (Dept. of Geriatric Medicine) and Prof. Michael Rowan (Dept. of Pharmacology, Trinity College Dublin). He completed a body of research on evoked potential electrophysiology and SPECT imaging in Alzheimer’s disease, resulting in an MD degree awarded by the National University of Ireland in 1993. He moved to Oxford, UK, in 1993 and completed senior registrar training in the Oxfordshire Area Health Authority training scheme. He was subsequently appointed to University of Birmingham as Senior Lecturer/Consultant in Geriatric Medicine in 1995 with a clinical base at the Queen Elizabeth Hospital, Edgbaston. He returned to CUH as consultant physician in Geriatric Medicine in 1999. In 2005, he was appointed as Senior Lecturer to the UCC Department of Medicine, with his clinical base as consultant physician continuing in CUH. He was promoted to Associate Professor in the UCC Department of Medicine in 2014. In 2024, he was awarded a DSc degree by the National University of Ireland in recognition of his contribution to research in clinical pharmacology in older people. In 2025, he was elected to the Royal Irish Academy.

Since 2005, he has led a multidisciplinary programme of research focusing on inappropriate prescribing in older people with chronic multimorbid illness and associated polypharmacy, now a well-recognized public health problem in the 21st century. He is the original inventor and principal developer of the STOPP/START criteria for inappropriate prescribing in late life. STOPP/START criteria are now recognized internationally and are the most widely used practical rules of good prescribing in older people, particularly in Europe. He has led, as principal investigator (PI), two major multi-centre clinical trials called SENATOR and OPTIMATE and has contributed as co-PI on another multi-centre trial called OPERAM examining the efficacy of STOPP/START criteria as an intervention in multimorbid older people in hospital. He has had several international research collaborations with senior academic colleagues in 7 different European countries, Canada and the USA. He has also had a leadership role in the development of other related screening tools for detection of inappropriate medications in particular clinical practice areas such as frailty (STOPPFrail), falls (STOPPFall) and dementia (STOPPCog). For the last 3 years, he has been rated as the world’s leading expert on Inappropriate Prescribing on Expertscape, based on approximately 4500 articles published in peer reviewed journals since 2013 (http://expertscape.com/ex/inappropriate+prescribing). To date, he has over 250 peer-reviewed publications (including books and numerous book chapters) and his research work has been widely cited in the scientific literature: his current H-index is 56. To date, his research has leveraged €20.4M in funding from national and international research funding agencies.

In December 2024, he took up the role of first director of research for the new HSE Southwest region (one of six in the new HSE regional structure). His new remit is to promote and direct clinical research through a network of hospitals and community care centres in Cork and Kerry.

Degrees: MB BCh BAO (Hons), MD, DSc

Diplomas: MRCPI, FRCPI

Other: MRIA