Tirzepatide (Mounjaro) was first approved as a treatment for type 2 diabetes before gaining recognition for weight management. Its powerful effects on blood glucose are central to how the medication works — and relevant even if you do not have diabetes.
The Mechanism
Mounjaro acts as a dual GIP and GLP-1 receptor agonist. Both of these incretin hormones play crucial roles in glucose regulation:
- GLP-1 activity: Stimulates the pancreas to release insulin in response to food (glucose-dependent insulin secretion), suppresses glucagon release (which reduces the liver's glucose output), and slows gastric emptying.
- GIP activity: Enhances insulin secretion and may improve the pancreas's sensitivity to glucose signals. The dual action is believed to be why Mounjaro achieves superior blood sugar reductions compared to GLP-1-only drugs.
Crucially, this insulin stimulation is glucose-dependent, meaning it primarily activates when blood sugar is elevated. This makes hypoglycaemia (dangerously low blood sugar) less likely compared to some older diabetes medications like sulphonylureas.
For Type 2 Diabetes Patients
Clinical trials (SURPASS programme) demonstrated that Mounjaro reduced HbA1c by up to 2.4 percentage points — a remarkable result. Many participants achieved an HbA1c below 48 mmol/mol, which is the threshold for diabetes remission. If you take Mounjaro for diabetes:
- Monitor your blood sugar regularly, especially when starting or increasing doses
- Your GP or diabetes nurse may need to reduce or stop other diabetes medications (particularly sulphonylureas or insulin) to prevent hypoglycaemia
- Report any episodes of low blood sugar (shakiness, sweating, confusion, dizziness) promptly
For Weight Management Patients Without Diabetes
Even if you do not have type 2 diabetes, Mounjaro affects your blood sugar. You may notice:
- More stable energy levels throughout the day (fewer sugar crashes)
- Reduced cravings for sugary foods
- Occasional lightheadedness if you skip meals, as blood sugar may dip lower than your body is accustomed to
This is generally beneficial, but it reinforces the importance of eating regular, balanced meals rather than going long periods without food.
Hypoglycaemia Awareness
While Mounjaro alone rarely causes dangerous hypoglycaemia, the risk increases if combined with other glucose-lowering medications, excessive alcohol consumption, or prolonged fasting. Symptoms include:
- Trembling and shakiness
- Sweating and feeling cold
- Irritability and confusion
- Rapid heartbeat
If you experience these symptoms, consume a fast-acting sugar source such as glucose tablets, fruit juice, or jelly babies, and follow up with a complex carbohydrate snack.
Regular monitoring and open communication with your prescriber ensure that Mounjaro's blood sugar effects remain beneficial rather than problematic.