A key point FPs need to watch for in patients using GLP-1s
We are losing our patients and loved ones to colon cancer. We don’t have to look far to see the rise in colorectal cancer over the last 10 to 15 years.
In my work in family medicine, individualizing cancer screening remains paramount for early detection. My radars for a first colonoscopy surveillance start as early as age 40 for those with a first degree family history of colorectal cancer or concerning polyps and/or a personal history of significant change in bowel pattern with or without rectal bleeding. Thankfully, the colon cancer screening guidelines have caught up and now support average risk screening from age 45—but we still have a lot of detective work ahead when it comes to preventative cancer screening.
I am now even more apprehensive and vigilant since GLP-1s have become mainstream for weight loss and diabetes management. On one hand, these medications are dramatically effective for weight reduction and optimize cardiometabolic health and this should translate to lower cancer risk over time. On the other hand, GLP-1s cause symptoms that mimic cancer by intentionally altering satiety and making people feel full on very little amounts of food. Their common effects include loss of appetite, rapid weight loss, fluctuations in bowel patterns—especially constipation as well as gastroparesis, nausea, and vomiting and these all become more pronounced with higher doses.
Another concerning effect is that GLP-1s can indirectly cause nutritional deficiencies including an iron deficiency or iron deficiency anemia by lowering appetite and subsequent food intake which is yet another masking red flag symptom requiring prompt referral for colonoscopy and other investigations.
I write to all my colleagues to weigh carefully when deciding to use a GLP-1. Over the last few years, I have become more cautious using them in patients with a history of bowel, renal, prostate, breast, ovarian and other cancers. I have also seen patients lean on excessive laxative use to overcome the constipation these drugs can cause which is yet another masking issue where colorectal cancer is concerned. Patients often under-report laxative use because they think it is the norm for managing this side effect. We all know stimulant and osmotic laxatives can dangerously conceal the obstructing effect of a colorectal mass and in the setting of a GLP-1, this approach to treating constipation can become normalized by both patient and physician which is another red flag in itself.
When starting a patient on a GLP-1 or if already started at another venue such as a bariatric or metabolic clinic or with an endocrinologist, or elsewhere, take a full cancer history and make sure colon cancer surveillance is up to date. Ask directly about laxative use and check for nutritional deficiencies including an iron deficiency or related anemia. If there’s a significant constipation history, reduce or remove the medication completely and monitor for a return to baseline functioning.
We all want our patients to achieve optimal metabolic health, but we have to balance with keeping our vigilance for cancer screening sharper than ever. We need to carefully monitor higher-risk age groups where cancer is concerned, adjust our history taking and document all changes reported by the patient including changes in bowel habits and potential laxative use. We need to as well, keep on the look out for potential nutritional deficiencies that GLP-1s indirectly trigger including iron deficiency anemia which further prompts the need for a colonoscopy and other investigations. Making these adjustments will help justify using these medications more cautiously as we try our best to keep our diagnostic and detective edge sharp in cancer detection.
We are still early in understanding the long-term risk profile of GLP-1s. I wish everyone continued vigilance in the pursuit of cancer prevention and screening while keeping in mind the inevitable and increasingly frequent first request of a GLP-1 and the potential implications that may arise from opening this new Pandora’s box.
Dr. Olivia Sankat is a family physician practising in Etobicoke, Ont.