Division of Gastroenterology

Grigorios I. Leontiadis


Associate Professor, Division of Gastroenterology, Department of Medicine

Member, Farncombe Family Digestive Health Research Institute





Education and Professional Standing

Dr. Leontiadis is an Associate Professor of Medicine, Division of Gastroenterology at McMaster University and consultant gastroenterologist at Hamilton Health Sciences in Hamilton Ontario.

He qualified from Aristotle University of Thessaloniki, Greece in 1992 and trained in Gastroenterology in Greece (Papanikolaou Hospital, Thessaloniki) and in the UK (Royal Albert Infirmary, Wigan and Queen Elizabeth Hospital, Gateshead).  He was awarded a PhD in 2002 from the Democritus University of Thrace, Greece. He worked for a short period as a Consultant Gastroenterologist at the University Hospital of North Durham, UK and then moved to Greece where he worked in private practice while being a Research Associate at the Aristotle University of Thessaloniki. In 2006 he was appointed Consultant Gastroenterologist & Senior Lecturer in Internal Medicine at the Democritus University of Thrace, Alexandroupolis. In 2008 he moved to McMaster University.

He is a Full Member of the Farncombe Family Digestive Health Research Institute, member of the steering committee of the MacGRADE Centre, and member of the HE&I (Department of Health Research Methods, Evidence, and Impact) Guideline Interest Group. He is the Coordinator for Residents’ Clinical Research at the Division of Gastroenterology. He is Joint Coordinating Editor for the Upper GI and Pancreatic Diseases Cochrane Group and Associate Editor for the American Journal of Gastroenterology and the Journal of Canadian Association of Gastroenterology. He is a member of the Guideline Committee of the World Organization of Gastroenterology and a guideline methodologist for the American Association of Gastroenterology and the Canadian Association of Gastroenterology (CAG). He served as Lead for Practice Affairs at CAG (2013-2018) responsible for ongoing clinical training, clinical practice-related issues, lobbying governmental agencies, knowledge dissemination and clinical practice guidelines. Since 2018 he is VP Clinical Affairs at CAG, overseeing the sections of Practice Affairs, Endoscopy, Regional Representation and Pediatric Gastroenterology.

His clinical and research interests include peptic ulcer disease, gastric acid suppression, H. pylori infection, gut microbiome, evolutionary medicine, systematic review and meta-analysis methodology, clinical practice guideline methodology (especially with regards to the appraisal of the quality of evidence with GRADE) and clinical epidemiology overall. He has published 4 book chapters and more than 80 peer-reviewed academic papers.

Selected Publications

  1. Leontiadis GI, Sharma VK, Howden CW. Non-gastrointestinal tract associations of Helicobacter pylori infection. Arch Intern Med 1999;159:925-40.
  2. Leontiadis GI, Minopoulos GI, Maltezos E, Kotsiou S, Manolas KI, Simopoulos K, Hatseras D. Effects of Helicobacter pylori infection on gastric emptying rate in patients with non-ulcer dyspepsia. World J Gastroenterol 2004;10:1750-4.
  3. Leontiadis GI, Sharma VK, Howden CW. Systematic review and meta-analysis of proton pump inhibitor therapy in peptic ulcer bleeding. BMJ 2005;330:568.
  4. Leontiadis GI, Sreedharan A, Dorward S, Barton P, Delaney B, Howden CW, Orhewere M, Gisbert J, Sharma VK, Rostom A, Moayyedi P, Forman D. Systematic reviews of the clinical effectiveness and cost-effectiveness of proton pump inhibitors in acute upper gastrointestinal bleeding. Health Technol Assess 2007;11(51):1-164.
  5. Barkun AN, Bardou M, Kuipers EJ, Sung J, Hunt RH, Martel M, Sinclair P; International Consensus Upper Gastrointestinal Bleeding Conference Group (Agreus L, Armstrong D, Calvet X, Chiba N, Cipolletta L, Cohen H, Enns R, Ericsson L, Gralnek I, Jensen D, Kaminishi M, Kanwal F, Laine L, Lanas A, Lau J, Leontiadis G, Lundell L, Malfertheiner P, Marshall J, Martin J, Metz D, Moayyedi P, Quenot JP, Rauws E, Romagnuolo J, Rostom A, Spiegel B, Tse F, Van Leerdam M, Van Rensburg C, Jones D, Gardeazabal A). International consensus recommendations on the management of patients with nonvariceal upper gastrointestinal bleeding. Ann Intern Med 2010;152:101-13.
  6. Armstrong D, Barkun A, Bridges R, Carter R, de Cara C, Dube C, Enns R, Hollingworth R, MacIntosh D, Borgaonkar M, Forget S, Leontiadis G, Meddings J, Cotton P, Kuipers E, Valori. Canadian Association of Gastroenterology consensus guidelines on safety and quality indicators in endoscopy. Can J Gastroenterol 2012;26:17-31.
  7. Leontiadis GI, Molloy-Bland M, Moayyedi P, Howden CW. Effect of comorbidity on mortality in patients with peptic ulcer bleeding: systematic review and meta-analysis. Am J Gastroenterol 2013;108:331-45.
  8. Tse F, Yuan Y, Moayyedi P, Leontiadis GI. Guide wire-assisted cannulation for the prevention of post-ERCP pancreatitis: a systematic review and meta-analysis. Endoscopy 2013;45:605-18.
  9. Neumann I, Letelier LM, Rada G, Claro JC, Martin J, Howden CW, Yuan Y, Leontiadis GI. Comparison of different regimens of proton pump inhibitors for acute peptic ulcer bleeding. Cochrane Database Syst Rev 2013;(6):CD007999.
  10. Moayyedi P, Yuan Y, Leontiadis G; CAG Clinical Affairs. Canadian Association of Gastroenterology position statement: hip fracture and proton pump inhibitor therapy- A 2013 update. Can J Gastroenterol 2013;27:593-5.
  11. Singh H, Leontiadis GI, Hookey L, Enns R, Bistritz L, Rioux LC, Hope L, Sinclair P; Canadian Association of Gastroenterology. Canadian Association of Gastroenterology policy on the application for, and implementation of, clinical practice guidelines. Can J Gastroenterol Hepatol 2014;28:473-80.
  12. Nguyen GC, Bernstein CN, Bitton A, Chan AK, Griffiths AM, Leontiadis GI, Geerts W, Bressler B, Butzner JD, Carrier M, Chande N, Marshall JK, Williams C, Kearon C. Consensus statements on the risk, prevention, and treatment of venous thromboembolism in inflammatory bowel disease: Canadian Association of Gastroenterology. Gastroenterology 2014;146:835-848.
  13. Yang YX, Brill J, Krishnan P, Leontiadis G; American Gastroenterological Association Clinical Practice Guidelines Committee. American Gastroenterological Association Institute Guideline on the role of upper gastrointestinal biopsy to evaluate dyspepsia in the adult patient in the absence of visible mucosal lesions. Gastroenterology 2015;149:1082-7. 
  14. Allen JI, Katzka D, Robert M, Leontiadis GI. American Gastroenterological Association Institute Technical Review on the role of upper gastrointestinal biopsy to evaluate dyspepsia in the adult patient in the absence of visible mucosal lesions. Gastroenterology 2015;149:1088-118.
  15. Bressler B, Marshall JK, Bernstein CN, Bitton A, Jones J, Leontiadis GI, Panaccione R, Steinhart AH, Tse F, Feagan B; Toronto Ulcerative Colitis Consensus Group. Clinical practice guidelines for the medical management of non-hospitalized ulcerative colitis: The Toronto consensus. Gastroenterology 2015;148:1035-1058.
  16. Nguyen GC, Seow CH, Maxwell C, Huang V, Leung Y, Jones J, Leontiadis GI, Tse F, Mahadevan U, van der Woude CJ; IBD in Pregnancy Consensus Group. The Toronto Consensus Statements for the Management of Inflammatory Bowel Disease in Pregnancy. Gastroenterology 2016;150:734-757.
  17. Fallone CA, Chiba N, van Zanten SV, Fischbach L, Gisbert JP, Hunt RH, Jones NL, Render C, Leontiadis GI, Moayyedi P, Marshall JK. The Toronto Consensus for the treatment of Helicobacter pylori infection in adults. Gastroenterology 2016;151:51-69
  18. Leontiadis GI. How to interpret a negative study. Am J Gastroenterol 2016;111:1506-1507.
  19. Enns RA, Hookey L, Armstrong D, Bernstein CN, Heitman SJ, Teshima C, Leontiadis GI, Tse F, Sadowski D. Clinical Practice Guidelines for the use of video capsule endoscopy. Gastroenterology 2017;152:497-514
  20. Chey WD, Leontiadis GI, Howden CW, Moss SF. American College of Gastroenterology Clinical Guideline: Treatment of Helicobacter pylori infection. Am J Gastroenterol 2017;112:212-23.