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Dr. John Lah, MD

Gastroenterologist
3851 Katella Ave, Ste 205, Los Alamitos, CA
4.66
“I would definitely recommend Dr Lah. Unlike many physicians, he was patient, super informative without me having to ask, gave his recommendation of what to take and why some differed etc. And high on the list was his timeliness.”
Susy C.October 8, 2026
Excellent wait time
97% of patients waited less than 30 minutes
New patient appointments
Appointments available for new patients

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About Dr. John Lah

Dr John J. Lah is a highly skilled, experienced gastroenterologist and former chief of GI at PIH Whittier. There he served on clinical faculty for the family practice residency for over 13 years. Prior to his Whittier legacy, he was the associate chief of GI at Kaiser Permanente in Walnut Creek. He completed his GI fellowship at UC Irvine where he developed his interventional endoscopic skills including endoscopic mucosal resection of large polyps, luminal stent placement and ERCP. He has performed over 20,000 endoscopic procedures with minimal complication rates. He received multiple teaching awards as faculty for the family practice residency at PIH Whittier and values communicating well with his patients and colleagues. He enjoys helping patients get a better understanding of their conditions and being able to provide practical, efficient solutions for their care. Dr. Lah is hard working, conscientious, and committed to providing high quality, compassionate care. He remains up to date with most recent advances in gastroenterology and will be actively involved with clinical research related to exciting new medications and diagnostics technologies. He looks forward to serving the needs of his patients and community.

In-network insurances

99% of patients have successfully booked with these insurances
Aetna
BlueCross BlueShield
Cigna
Medicare
UnitedHealthcare

Areas of expertise

This doctor's experience enhances their expertise in similar cases. Below are the conditions or surgeries they treat most frequently.
Acid reflux
Upper GI endoscopy
Colonoscopy
Acid reflux
Upper GI endoscopy
Colonoscopy

Practice

United Medical Doctors

United Medical Doctors (UMD) is dedicated to improving the health of our communities by setting the standard of excellence in specialty medical & surgical care. UMD currently offers 50+ medical & surgical specialties with over 200 providers in 80+ locations across four Southern California counties: Riverside, Orange, San Diego & Los Angeles. Our specialties include: Acupuncture | Allergy | Anesthesia | Audiology | Bariatric Surgery | Breast Surgery | Cardiology | Clinical Research | Colorectal Surgery | Complex GI Surgery | Dermatology | Dietitian | Endocrine Surgery | Endocrinology | Family Medicine | Fitness | Foot & Ankle Specialist & Surgery | Gastroenterology | General Surgery | Gynecology | HPB Surgery | Hepatology | Imaging | Infusion Therapy | Internal Medicine | Medical Weight Loss | Men’s Health | Minimally Invasive Gynecologic Surgery | Neurosurgery | Oncology | Otorhinolaryngology (ENT) | Orthopaedic Surgery | Pain Management | Pathology | Pediatric Gastroenterology | Physical Therapy | Plastic Surgery | Psychiatry | Radiology | Spine Medicine | Sports Medicine | Urgent Care | Urogynecology & Female Pelvic Health | Urology | Wound Care
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Office locations

United Medical Doctors - Los Alamitos, Katella Ave (1 of 2)
3851 Katella Ave, Ste 205, Los Alamitos, CA 90720
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United Medical Doctors (2 of 2)
3840 Woodruff Ave, Ste.206, Long Beach, CA 90808
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1 of 2

Education and background

Board certifications

  • Gastroenterology (American Board of Internal Medicine)

Education and training

  • New York Medical College, Doctor of Medicine
  • University of California, Irvine, Fellowship in Gastroenterology
  • University of California, Irvine, Residency in Internal Medicine
  • University of California San Diego (Bachelor's)

Languages spoken

  • English

Provider's gender

Male

NPI number

1437221272

Patient reviews

Overall rating
4.66
Wait time
4.72
Bedside manner
4.78
Your trust matters. All reviews have been submitted by verified patients after seeing the provider. Any content containing private health information is not published.
70 reviews
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Dr. Lah seemed very competent and knowledgeable. My wife was with me and she saw it the same way. I'm glad we found him.
Verified patient
My visit was productive and focused on my needs and next steps for my condition.
Verified patient
The doctor is a great listener, and he communicates with the patient very well with professional expertise
Dr Lah was professional and friendly. He explained everything and was able to provide the needed care.
Verified patient
Doc was great, got me in right away, and made it as comfortable as could be expected.
Verified patient
Super helpful and answered all our questions with ease!
Verified patient
Made me feel very at ease and very understanding of my condition
Had a great appointment , would use this service again
Verified patient
He knew his stuff & we’re trying something new for me
Verified patient
Amazing professional. Very friendly and communicator
Verified patient
I would definitely recommend Dr Lah. Unlike many physicians, he was patient, super informative without me having to ask, gave his recommendation of what to take and why some differed etc. And high on the list was his timeliness.
Verified patient
Dr. Lah is very professional. He explains the issues in a straightforward manner. Office staff are very friendly and polite. Thanks
Verified patient
DrJohn Lah was very iinformative during my appointment. He answers all the health issues I asked him. He assisted me to the front desk for my next sppointment.
Verified patient
Dr. Lah was obviously knowledgeable, honest and a good communicator. He was clear that he wanted to review my files from my recently-retired gastroenterologist before commenting on my prior procedures. I felt like I was in good hands.
This visit was one of the best experiences with a physician appointment that I have ever had. I have already referred others to him.
Verified patient
Dr Lau was very methodical and provided as me details as possible to make me a more informed patient. I would definitely recommend Dr. Lau.
Verified patient
Dr. Lah was excellent! I would highly recommend him. I appreciate that he listened to me and that he appeared to genuinely care. I like the fact I didn’t feel rushed.
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