Mounjaro was not originally developed as a weight loss medication. Tirzepatide was first approved as a treatment for type 2 diabetes, weight management came second. This means the evidence base in diabetes is exceptionally strong. The answer is yes. Mounjaro is both licensed and clinically well-supported for type 2 diabetes. But there are important nuances around how it works in this population, which medications it interacts with, and what requires closer monitoring.

Why Mounjaro is particularly valuable in type 2 diabetes

In non-diabetic patients, tirzepatide primarily suppresses appetite and drives weight loss. In type 2 diabetes, it additionally addresses the core pathophysiology directly:

  • Stimulates insulin secretion in a glucose-dependent manner: only increases insulin when blood glucose is elevated, reducing hypoglycaemia risk compared to sulphonylureas
  • Suppresses glucagon: reducing the liver's inappropriate glucose output between meals
  • Reduces post-meal blood glucose spikes by slowing gastric emptying
  • Improves insulin sensitivity in peripheral tissues, addressing the core defect of type 2 diabetes
  • Produces significant weight loss: which independently improves insulin sensitivity and glycaemic control

In SURPASS-2 (Frías JP et al, N Engl J Med 2021, n=1,879), tirzepatide at all three doses was superior to semaglutide 1mg for both HbA1c reduction and weight loss. Tirzepatide 15mg reduced HbA1c by an average of 2.3 percentage points: exceeding the reduction seen with most existing diabetes medications.

How does weight loss compare in diabetic vs non-diabetic patients?

Important distinction. SURMOUNT-1 (non-diabetic patients) showed 22.5% average weight loss at 15mg over 72 weeks. SURMOUNT-2 (type 2 diabetes patients, Davies M et al, Lancet 2023) showed average weight loss of 13.4% at 10mg and 15.7% at 15mg over 72 weeks. Still substantial and clinically meaningful, but lower than the non-diabetic population. Patients with type 2 diabetes should be aware their expected results may be towards the lower end of the clinical trial range.

Interactions with other diabetes medications

Insulin: Combined with tirzepatide, the risk of hypoglycaemia is real. Insulin doses typically need to be reduced when tirzepatide is started, only under clinical supervision. Never reduce insulin independently. Your prescribing pharmacist or diabetes team will monitor and adjust.

Sulphonylureas (gliclazide, glipizide, glibenclamide): Cause insulin release regardless of blood glucose level. Combined with tirzepatide, hypoglycaemia risk increases. Dose reduction of the sulphonylurea is often required when tirzepatide is initiated.

Metformin: No significant interaction. Frequently used together with tirzepatide with good complementary effect. No dose adjustment typically required.

SGLT-2 inhibitors (dapagliflozin, empagliflozin): No significant interaction. Compatible with tirzepatide. Some patients benefit from continuing SGLT-2 inhibitors alongside Mounjaro, particularly those with cardiovascular or renal comorbidities.

DPP-4 inhibitors (sitagliptin, saxagliptin): Significantly overlap with tirzepatide's mechanism (both act on the GLP-1 pathway). Combining both is not recommended. The DPP-4 inhibitor is typically discontinued when tirzepatide is started.

Blood glucose monitoring

Patients with type 2 diabetes starting Mounjaro should monitor blood glucose more frequently during the initial weeks and after each dose increase. Particularly important for patients on insulin or sulphonylureas, proactive monitoring allows dose adjustment before hypoglycaemia occurs. Regular monitoring also guides HbA1c assessment and dose decisions.

HbA1c improvements

Beyond weight loss, tirzepatide produces significant HbA1c reductions, among the strongest of any available diabetes medication. For many patients, initiating Mounjaro may allow simplification of their diabetes treatment regimen, potentially reducing or eliminating the need for other medications, under medical supervision.

Is Mounjaro suitable for all patients with type 2 diabetes?

Standard contraindications apply: history of medullary thyroid carcinoma or MEN2, pancreatitis, allergy to tirzepatide, pregnancy. Type 1 diabetes: not indicated and carries risks. Severe gastroparesis: contraindicated, tirzepatide further slows gastric emptying and would exacerbate this condition. History of significant GI surgery: requires careful individual assessment.

NHS Mounjaro for diabetic patients

Tirzepatide is available on the NHS through specialist diabetes services for patients with type 2 diabetes, a separate pathway from the obesity management rollout. If you have type 2 diabetes and are not yet accessing NHS Mounjaro, speak to your diabetes specialist or GP about whether you qualify under the diabetes indication.

When to see your pharmacist or doctor
  • Before starting Mounjaro if you are on insulin, dose adjustment will be needed
  • If you are on a sulphonylurea, the combination increases hypoglycaemia risk
  • If you experience symptoms of hypoglycaemia: sweating, trembling, confusion, rapid heartbeat
  • Any new or worsening abdominal pain, pancreatitis risk
  • Before stopping any existing diabetes medication without guidance
  • If you have gastroparesis or a history of significant GI surgery

References

  1. Frías JP et al. N Engl J Med 2021;385:503 to 515 (SURPASS-2).
  2. Davies M et al. Lancet 2023 (SURMOUNT-2).
  3. Mounjaro Summary of Product Characteristics, Eli Lilly, 2024.
  4. NICE Technology Appraisal TA1026 (2024).

Reviewed by Jimah Alsaai MPharm, GPhC 2232652, Superintendent Pharmacist, Solira.