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DEAR DR. ROACH: I'm a 73-year-old female who has Type 1 diabetes that began as Type 2 diabetes more than 30 years ago. I have a very strong family history of coronary artery disease, and I personally have a cardiac stent. I use an insulin pump and have good control with carb counting. I struggle with my weight (160 pounds at 5 feet, 2 inches tall) and with controlling my insulin dose. My A1C is 5.8%. I have ocular hypertension and some diabetic retinopathy. I receive Avastin injections in my eye approximately every two years.
My physician has ordered Mounjaro for weight loss. My concerns are my diabetic retinopathy and the diagnosis of Type 1 versus Type 2 diabetes. What are your thoughts on the safety of starting Mounjaro? -- C.D.C.
ANSWER: Type 1 diabetes is very different from Type 2. Type 1 diabetes is often diagnosed in childhood or adolescence and is an autoimmune disease that attacks the cells in the pancreas (islet cells), which make insulin. People with Type 1 diabetes have very little to no insulin.
People with Type 2 diabetes make normal or even high amounts of insulin. With Type 2 diabetes, the primary problem is resistance to insulin. Insulin can be used, but newer therapies are designed to reduce insulin needs.
Many people with latent autoimmune diabetes in adults (LADA) are initially misdiagnosed with Type 2 diabetes, and I suspect that this is your actual diagnosis. A diagnosis of LADA is typically made after age 30. (It sounds like you had problems beginning around age 40.) There's no insulin requirement for at least six months, and blood tests confirm the presence of islet-cell antibodies. People with LADA usually have Type 1 diabetes.
You have disease in both the small blood vessels (Avastin is used for diabetic retinopathy, a small vessel disease) and large vessels (the stent in your coronary artery), which can happen with either type of diabetes but is consistent with Type 1. There's strong evidence that GLP-1 drugs are helpful in preventing heart attacks in people with Type 2 diabetes but not for those with Type 1 (although they still may be helpful).
Your question is about the use of tirzepatide (Mounjaro when used for diabetes) for Type 1 diabetes. Your A1C is in the nondiabetic range; I don't recommend new medication to lower your A1C further, so it seems like you'd be using it for weight. The expert opinion does recommend medicines like tirzepatide for weight loss in people with Type 1 diabetes who are obese, but your BMI of 29.3 doesn't meet the definition of obese.
So, there is a safety issue in that even modest doses of Mounjaro could cause a drop in your blood sugar. Having an insulin pump (especially when combined with a continuous glucose monitor) can reduce this risk. But if you do go on Mounjaro, you should pay careful attention and regulate your carbohydrate intake to avoid ketosis (ketones in the urine, which show inadequate cellular nutrition and put you at risk for diabetic ketoacidosis). The normal dose escalations used for obesity or for Type 2 diabetes may be too aggressive, so your doctor should increase the dose very slowly.
You may also be at a higher risk for the nausea and vomiting that is common among people taking GLP-1 agents, although most people with Type 1 diabetes did develop a tolerance to the drug. In summary, Mounjaro may be effective at helping you lose weight, although your blood sugar and ketone levels should be monitored by an expert.