Our physicians were trained at the top medical schools in the country. They are involved in cutting-edge research, have written textbooks, are published in peer-reviewed publications, and have lectured to physicians around the world. Our doctors have also been featured in national media such as Discovery Health, The Oprah Winfrey Show, The Doctors, The New York Times, People, Entertainment Tonight, The Insider, CNN, ABC News, Fox 11 News, and ELLE magazine and more.

Medical Director

Dr. Mark Davidson

Mark Davidson, MD

Mark Davidson, MD is board-certified in both Gastroenterology and Internal Medicine. Dr. Davidson is an Attending Physician at Cedars Sinai Medical Center and other local hospitals in Los Angeles, in addition to having his own gastroenterology practice. His practice focuses on clinical medicine and a variety of endoscopic procedures. Thousands of patients have trusted their medical care to Dr. Davidson for a variety of medical disorders but especially for screening of colon cancer.

Mark Davidson, M.D. received his medical degree from David Geffen School of Medicine at the University of California, Los Angeles (UCLA). He completed a three-year residency program in internal medicine at the UCLA-affiliated Veterans Affairs Medical Center in Los Angeles and finished a three-year fellowship program in Gastroenterology with emphasis on liver disorders at the UCLA-affiliated Kaiser Permanente Medical Center in Los Angeles.


Our Team of Doctors


Dr. Siamak TabibSiamak Tabib, MD

Siamak Tabib, MD is board-certified in Internal Medicine, Gastroenterolgy and Hepatology. Dr. Tabib incorporates both health maintenance and disease prevention in his practice of Gastroenterology and Hepatology. These two specialty fields of medicine deal primarily with conditions of the digestive tract. His goal is to maintain health primarily through disease prevention, and when necessary, to intervene with appropriate state of the art methods.

Dr. Payman KhorramiPayman Khorrami, MD

Payman Khorrami, MD is board-certified in Gastroenterology and Hepatology and has had the additional education to diagnose and treat complex gastrointestinal problems. He has been expertly trained to perform colonoscopies when they are required to determine the cause of a patient’s complaints, and has his own private practice in gastroenterology, liver disorders and nutrition. Dr. Khorrami has appeared on several television and radio talk shows to discuss disorders of the gastrointestinal tract.

Dr. Arash Ari NowainArash Ari Nowain, MD

Arash Ari Nowain, MD, co-director of the Colonoscopy Center of Excellence, is board-certified in gastroenterology and internal medicine and specializes in medical disorders of the digestive system. In addition to having his own private GI practice in Beverly Hills, Dr. Nowain treats acute and chronic GI problems with a heavy focus on prevention of colon cancer. Dr. Nowain has staff privileges at the Cedars-Sinai Medical Center and other local hospitals in Los Angeles. He is a Los Angeles native and is thrilled to practice where he grew up.

Dr. Leo TreyzonLeo Treyzon, MD, MS

Leo Treyzon, MD, MS is a board-certified gastroenterologist. He serves as the Chief of Gastroenterology at Cedars-Sinai in Los Angeles. He is also board-certified in clinical nutrition. Dr. Treyzon has a sub-specialization in nutrition and obesity. He serves on the Cancer Committee at Cedars Sinai Medical Center and is an active member in four Centers of Excellence at Cedars Sinai: Weight Loss Center, Esophageal Disorders Center, the Colorectal Cancer Center, and the Inflammatory Bowel Disease Center. Additionally, Dr. Treyzon has a private practice in gastroenterology.

Dr. Peyton BerookimPeyton Berookim, MD

Peyton Berookim, MD is board-certified by the American Board of Internal Medicine and Subspecialty Board of Gastroenterolgy. Dr. Berookim’s key areas of interest are colon cancer screening, surveillance, and prevention. As a member of the American College of Gastroenterology and the American College of Physicians, Dr. Berookim has placed special emphasis on continually educating himself on the latest and most advanced procedures and treatments in gastroenterology, in addition to having a practice at the Gastroenterology Institute of Southern California.

Dr. Maurice ElihuMaurice Elihu, MD

Dr. Maurice Elihu is a board-certified gastroenterologist that specializes in the comprehensive evaluation and prevention of colorectal cancers. He believes that the key to proper diagnosis and treatment is personal attention to every patient. Dr. Elihu is an active member of American College of Gastroenterology & Southern California Society of Gastroenterology as well as a Diplomate of the American Board of Internal Medicine and American Board of Gastroenterology. He also has his own private practice in gastroenterology and internal medicine.

Dr. Farshid Sam RahbarFarshid Sam Rahbar, MD

Farshid Sam Rahbar, MD is the leading integrative gastroenterologist in Los Angeles, California. He is board-certified in Gastroenterology, Internal Medicine, Integrative Holistic Medicine, and Anti-Aging, Regenerative, and Functional Medicine. Dr. Rahbar incorporates anti-aging & functional medicine for an integrative-holistic approach to digestive care. He brings over 20 years of excellent technical skills in endoscopy and colonoscopy along with a Holistic-Integrative approach to each.

Dr. Shabab MehdizadehShahab Mehdizadeh, MD

A co-director of the Colonoscopy Center of Excellence, Shahab Mehdizadeh, MD is board-certified in gastroenterology, internal medicine, and diseases of the liver. His research focuses on new and advanced endoscopic techniques with particular emphasis on prevention of cancers of the colon. Dr. Mehdizadeh greatly values the importance of nutrition in the treatment and prevention of disorders. He is board certified by the American Board of Physician Nutrition Specialists, and has his own practice in Beverly Hills.

Dr. Eiman FiroozmandEiman Firoozmand, MD

Eiman Firoozmand, M.D. is board certified in colorectal and general surgery. He is currently Chief of the Division of Colorectal Surgery at Cedars-Sinai Medical Center in Beverly Hills. Dr. Firoozmand’s main practice involves treatment of colon and rectal cancer. Dr. Firoozmand has written numerous articles for peer-reviewed publications including The American Surgeon, The Journal of Trauma, and Surgical Laparoscopy & Endoscopy.

Dr. Liza M. CapiendoLiza M. Capiendo, MD

Liza M. Capiendo, MD is board-certified by and a member of The American Society of Colon and Rectal Surgeons. Dr. Capiendo has published the results of her original research on the Radiotherapeutic Pretreatment of Colon Xenografts in The Journal of Immunopharmacology and has also presented the results of her investigation into recurrent colon and rectal cancer to The American Society of Colon and Rectal Surgeons Convention in Philadelphia. Dr. Capiendo has her own practice that specializes in colon and rectal surgeries. She is also the Clinical Chief of the Department of Colon and Rectal Surgery at Cedars Sinai Medical Center.

Dr. Gary HoffmanGary Hoffman, MD

Gary Hoffman, MD is a board-certified colorectal surgeon. He is a member of The American Society of Colon and Rectal Surgeons, Southern California Society of Colon and Rectal Surgeons, The American College of Surgeons and The American Medical Association. Dr. Hoffman’s main clinical and research interests involve the laparoscopic, minimally invasive treatment of colon and rectal malignancies. He has been published the peer-reviewed Diseases of the Colon and Rectum and Surgical Rounds, and has his own practice focusing on colon and rectal surgery.

Benjamin Basseri, MDBenjamin Basseri, MD

Benjamin Basseri, MD is a gastroenterologist who specializes in the evaluation and management of difficulty swallowing (dysphagia), indigestion (dyspepsia), abdominal pain, irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer screening. Dr. Basseri is also an active member of the American Gastroenterological Association, American College of Gastroenterology, and American Society for Gastrointestinal Endoscopy.

Dr. Magner Colonoscopy MD

David P. Magner, MD

Dr. Magner is board-certified in minimally-invasive and laparoscopic colon and rectal surgery. Through an interdisciplinary, patient-centered approach, Dr. Magner specializes in the treatment of all aspects of colorectal disease. Dr. Magner’s expertise includes pelvic floor dysfunction, benign anorectal conditions, advanced gastrointestinal malignancies, and inflammatory bowel disease.

MakhaniMarc D. Makhani, MD

Dr. Marc D. Makhani is a gastroenterologist who is native of Los Angeles. Dr. Makhani centers his principles on a passion for promoting overall health and wellbeing. Dr. Makhani has a wide range of clinical and research interests that include colon cancer screening and prevention, motility disorders of the gastrointestinal tract, gastroesophageal reflux disease, peptic ulcer disease, irritable bowel syndrome and inflammatory bowel disease.


Maziar Ghodsian, MD

Dr. Maziar Ghodsian, or Dr. Maz, as he is so kindly referred to by his patients, is a highly specialized Proctologist and Colorectal Endoscopist. He specializes in diseases of the colon and rectal surgery as well as aesthetic anal beautification and rejuvenation. Dr. Maz also performs diagnostic and therapeutic colonoscopies for colon cancer and rectal cancer.

Dr. Maz obtained his Bachelor of Science in Biology and a Minor in Philosophy from the University of California, Riverside. Dr. Maz continued his training at the Johns Hopkins University, where he received a second Bachelor of Science in Nursing followed by a Juris Doctor with a concentration on Healthcare Law and Policy from the Pace University School of Law. He then attended medical school at Western University of Health Sciences in Southern California and completed his internship at Arrowhead Regional Medical Center. Dr. Maz completed his residency training in Proctologic Surgery at Ohio University-Grandview Medical Center/Kettering Health Network in Dayton, Ohio. Additionally, Dr. Maz completed a portion of his residency training in Proctologic Surgery at the Cleveland Clinic Foundation and Cedars Sinai Medical Center with world renowned experts. Dr. Maz is a Board Member of the American Osteopathic College of Proctology.

Dr. Maz is one of only two practicing Proctologic Surgeons in California that have completed a residency in Proctology.

Using his specialized minimally invasive and aesthetic approach, Dr. Maz uses exceptional technical skills in treating his patients with both surgical and non-surgical treatment modalities. Dr. Maz is highly specialized in the cosmetic removal of anal skin tags, lesions, warts and hemorrhoids.

Contact Our IBD Experts

We offer a range of the most experienced and knowledgeable surgeons that specialize in IBD. While the majority of our patients prefer to come to our outpatient surgery center for their procedures, you can also opt for surgery at Cedars Sinai, where many of our doctors also perform surgery. Please contact us to learn more about Cedars Sinai IBD treatment, or treatment at our outpatient facilities. You can reach our office by phone at (888) 421-4172 or by filling out our online contact form. We look forward to providing you high quality patient care.

Next, read about our facilities.