Unlike some of the other conditions people ask about alongside Mounjaro, insulin resistance is closely linked to how this medicine works and its use in type 2 diabetes and weight management. Mounjaro may improve insulin sensitivity and blood sugar control by activating GIP and GLP 1 receptors. Weight loss during treatment may also improve insulin sensitivity, particularly when there is a reduction in excess body fat. For adults in the UK who are managing type 2 diabetes or weight related health concerns, it is useful to understand how Mounjaro works before comparing treatment options or setting expectations.
This is one topic where understanding the actual mechanism and clinical evidence is more useful than vague descriptions of "biological processes". This guide explains how Mounjaro works, what clinical trials have found, how it compares with insulin, what "improving" or "reversing" insulin resistance may mean, and why lifestyle factors still matter alongside treatment.
Key things to know
- Mounjaro is licensed for type 2 diabetes as well as weight management, and its effects on blood sugar and insulin sensitivity are relevant to both uses
- Its dual GIP and GLP 1 action can support the body's response to insulin and help improve blood sugar control
- Mounjaro is not insulin and works differently, although clinical trials have compared tirzepatide with insulin in people with type 2 diabetes
- Clinical trials have shown meaningful HbA1c improvements and, in some head to head trials, better blood sugar control than the insulin treatments used in those studies, with less weight gain
The rest of this guide looks at how Mounjaro works, what the trial results actually show, and what "reversing" insulin resistance may realistically mean.
What Insulin Resistance Actually Is
Insulin resistance happens when the body's cells do not respond as well to insulin, the hormone that helps move glucose from the blood into cells for energy. The pancreas may respond by producing more insulin to help keep blood glucose levels within range. Over time, if the pancreas cannot produce enough insulin to meet the body's needs, blood glucose levels can rise and type 2 diabetes may develop.
Insulin resistance is often linked with excess weight, particularly excess visceral fat. Visceral fat is stored around internal organs and is metabolically active. It can affect how the body responds to insulin through hormonal and inflammatory signals.
Insulin resistance can also affect how the body processes glucose and how much glucose the liver releases into the bloodstream. It is linked with conditions such as type 2 diabetes and metabolic syndrome.
This connection can work in both directions. Excess visceral fat can contribute to insulin resistance, while insulin resistance can make blood sugar and weight management more difficult. This is one reason why treatment plans often consider blood sugar, weight, diet and physical activity together rather than treating them as completely separate issues.
How Mounjaro Actually Improves Insulin Sensitivity
Mounjaro contains tirzepatide, which activates two hormone receptors called GIP (glucose dependent insulinotropic polypeptide) and GLP 1 (glucagon like peptide 1). These are linked to the body's natural incretin system, which helps regulate blood glucose and insulin after eating.
Activating these receptors can increase insulin release when blood glucose is elevated and reduce glucagon levels. This helps the body regulate blood glucose more effectively. The glucose dependent action means the effect on insulin release is linked to blood glucose levels, although low blood sugar can still occur, particularly when Mounjaro is used with certain other diabetes medicines.
Mounjaro may improve insulin sensitivity through more than one pathway. Its effects on GIP and GLP 1 receptors support the body's natural response to glucose. Weight loss during treatment may also improve insulin sensitivity, particularly when excess visceral fat is reduced.
These effects work alongside each other rather than being completely separate processes. However, the extent of any improvement can vary from person to person.
The dual GIP and GLP 1 action is one of the features that distinguishes tirzepatide from medicines that activate GLP 1 receptors alone. Clinical research has shown improvements in measures of blood sugar control and insulin sensitivity with tirzepatide. The timing and extent of these changes can vary between individuals.
Is Mounjaro Insulin?
No. Insulin is a hormone that can be given by injection to directly lower blood glucose. Mounjaro works differently. It activates GIP and GLP 1 receptors to support the body's own insulin response when blood glucose is elevated, while also affecting appetite, food intake and digestion.
Both medicines can be used in type 2 diabetes management, and they may sometimes be prescribed as part of the same treatment plan. However, they are different medicines with different mechanisms.
The confusion is understandable because both are injectable treatments used in diabetes care and both affect blood glucose. The key difference is that insulin supplies insulin directly, while Mounjaro helps the body regulate its own insulin response.
They also have different side effect profiles. Mounjaro can cause side effects such as nausea, vomiting, diarrhoea and constipation. More serious side effects can occur, including pancreatitis. Mounjaro is also not suitable for people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN2), in line with its prescribing information.
The risk of low blood sugar can also differ depending on the treatment being used and whether Mounjaro is taken with other medicines that can cause hypoglycaemia. This is one reason why treatment choices should be based on an individual's medical circumstances rather than a simple comparison between medicines.
What the Trial Data Actually Shows
Clinical trials provide useful evidence about how tirzepatide performs in specific groups of people. In the SURPASS 4 trial, tirzepatide was compared directly with insulin glargine over 52 weeks in people with type 2 diabetes. At the 15mg dose, HbA1c fell by 2.58 percentage points with tirzepatide compared with 1.44 percentage points with insulin glargine. Average body weight changed by -11.7kg with tirzepatide compared with a 1.9kg gain with insulin glargine. Tirzepatide was also associated with a lower rate of hypoglycaemia in this study.
Clinical studies in people using tirzepatide for weight management have also reported body weight reductions of up to 22.5% at the maximum dose in some study groups. This is a study result and should not be treated as a prediction of how much weight an individual will lose.
A separate study, SURPASS 6, compared tirzepatide with insulin lispro added to existing basal insulin in people with type 2 diabetes. Tirzepatide reduced HbA1c by 2.1 percentage points compared with 1.1 percentage points with insulin lispro. These results were seen in the specific trial population and treatment setting studied.
It is important to understand what these results do and do not tell you. They show how tirzepatide performed against particular insulin treatments in specific clinical trials. They do not mean that Mounjaro is always a better choice than insulin. Insulin remains an important treatment for many people with diabetes, and it may be necessary in situations where tirzepatide is not appropriate.
Research has also reported improvements in fasting insulin and HOMA IR, which are measures that can help assess insulin resistance. Tirzepatide may also affect other metabolic measures, such as blood pressure and cholesterol, although individual responses vary.
| Trial | Comparison | HbA1c Change (15mg tirzepatide) | Weight Change |
|---|---|---|---|
| SURPASS 4 | vs insulin glargine, 52 weeks | -2.58 percentage points (vs -1.44) | -11.7kg (vs +1.9kg gain) |
| SURPASS 6 | vs insulin lispro (added to basal insulin) | -2.1 percentage points (vs -1.1) | Not the primary comparison point |
If you are weighing up Mounjaro against insulin specifically for type 2 diabetes, our Mounjaro vs insulin guide covers this comparison in more detail.
Does Mounjaro Reverse Insulin Resistance?
"Reverse" is a strong word, so it is worth being careful with it. Mounjaro may improve insulin sensitivity, insulin resistance and blood sugar control, as shown by clinical research. For some people, this may lead to substantial improvements in metabolic health.
Whether this should be described as a full "reversal" depends on factors such as the person's health, how long insulin resistance has been present, weight, genetics and lifestyle. It is more accurate to talk about improvement in insulin sensitivity and blood sugar control rather than promise complete reversal for everyone.
This distinction matters when setting realistic expectations. Someone with early insulin resistance may see a substantial improvement in blood sugar and insulin sensitivity with treatment and lifestyle changes. Some people with type 2 diabetes may also have their diabetes medicines adjusted as their blood glucose improves, but this should only happen under the supervision of a healthcare professional.
Someone with long standing insulin resistance or established type 2 diabetes may also experience meaningful improvements without their insulin sensitivity returning completely to its previous level. The response to treatment is individual, so regular monitoring remains important.
If you would like to discuss Mounjaro treatment for insulin resistance or type 2 diabetes, start your free consultation with a UK prescriber.
Lifestyle Factors Still Matter Alongside Treatment
Mounjaro is used alongside a reduced calorie diet, increased physical activity and healthy lifestyle habits. It is not intended to replace these measures.
Physical activity can support insulin sensitivity independently of weight loss. When muscles are active, they can take up glucose from the blood and use it for energy. Regular activity can therefore be an important part of managing blood glucose and metabolic health.
Clinical trials of Mounjaro were carried out alongside diet and lifestyle advice, so the results should not be interpreted as the effect of medication completely separate from lifestyle support.
Building sustainable habits around food, physical activity and other aspects of your health can support weight management and blood sugar control during treatment. These habits can also remain important if your treatment plan changes in the future.
Sources
- Frías JP et al., SURPASS 4 trial: Tirzepatide compared with insulin glargine in patients with type 2 diabetes, The Lancet, 2021
- Rosenstock J et al., SURPASS 6 trial: Tirzepatide vs insulin lispro added to basal insulin, JAMA, 2023
- NICE Technology Appraisal TA924: Tirzepatide for treating type 2 diabetes
Medical Disclaimer
This page provides general information about Mounjaro and insulin resistance. It is not a substitute for personalised medical advice, diagnosis or treatment. Whether Mounjaro is appropriate for you should be assessed by a prescriber as part of an individual clinical assessment. This may include considering your blood glucose levels, diabetes history, current medicines and other health factors.
The trial results mentioned on this page come from specific study populations and treatment settings. They should not be treated as a guarantee of the same results for every person.
Mounjaro may not be suitable for everyone. Tell your prescriber about your medical history, current medicines and any health conditions before starting treatment. If you have questions about your treatment, speak to your prescriber, pharmacist or GP. Continue with any recommended follow up and monitoring throughout your treatment.