By Dr. Asnat Raziel, bariatric surgeon specializing in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal, Tel Aviv
Mounjaro (tirzepatide): what to know before you start
Mounjaro (tirzepatide) is a once-weekly injection for obesity and type 2 diabetes. In the major clinical trials, it produced an average weight loss of up to 20.9% of body weight. It also improves blood sugar control, blood pressure and blood lipids, which is why many experts now consider it one of the most effective medications in the field.
Eli Lilly developed the drug, and regulators first approved it for diabetes. However, it soon became clear that it also has a powerful effect on weight. In the United States, Lilly markets the same active ingredient for obesity under the name Zepbound. Israel, however, uses the name Mounjaro for both indications. In this guide, I have gathered the most up-to-date data.
How Mounjaro (tirzepatide) works
Mounjaro acts on the receptors of two natural satiety hormones. The first is GIP (glucose-dependent insulinotropic polypeptide), a gut hormone that stimulates insulin release in response to blood sugar levels. The second is GLP-1 (glucagon-like peptide-1), a satiety hormone released by the gut after a meal. In other words, tirzepatide is a dual agonist, not just a GLP-1 agonist like Wegovy and Ozempic.
This dual action affects several systems at once:
- It increases satiety and reduces hunger and the urge to eat.
- It quiets “food noise,” those intrusive, persistent thoughts about food.
- It boosts insulin release only when blood sugar is high.
- It reduces glucagon secretion and slows stomach emptying.
Most of the effect on weight comes from the hunger and satiety centers in the brain. I explore the link between these medications and the brain in more depth in my article on how the new obesity drugs work in the brain.
Who is the treatment for?
Mounjaro is intended for adults with obesity, meaning a BMI (body mass index) of 30 or higher. It is also suitable for people with a BMI of 27 or higher who have a weight-related condition, such as high blood pressure, diabetes, abnormal blood lipids or fatty liver. In addition, it is approved for the treatment of type 2 diabetes. Your doctor always decides whether to start treatment after a full medical evaluation.
How much weight can you lose with Mounjaro (tirzepatide)?
The SURMOUNT trial program tested the drug in thousands of participants, all of whom also received diet and exercise counseling. The key results:
- Without diabetes: The SURMOUNT-1 trial enrolled 2,539 adults. After 72 weeks, average weight loss was 15.0% on the 5 mg dose, 19.5% on 10 mg and 20.9% on 15 mg. In the placebo group, weight loss was only 3.1%.
- With type 2 diabetes: In the SURMOUNT-2 trial, weight loss was 12.8% on 10 mg and 14.7% on 15 mg, compared with 3.2% on placebo. This matters because losing weight is generally harder for people with diabetes.
- After lifestyle change: In the SURMOUNT-3 trial, participants first lost an average of 6.9% on an intensive lifestyle program. Mounjaro then added a further 18.4% weight loss, while the placebo group regained 2.5%.
Keep in mind that these are averages. In other words, some patients lose more, and some lose less. I explain why in my article on why weight-loss injections don’t work for everyone.
Mounjaro vs. Wegovy: the head-to-head comparison
The SURMOUNT-5 trial was the first to compare the two drugs directly. It enrolled 751 adults with obesity and without diabetes. After 72 weeks, tirzepatide produced an average weight loss of 20.2%, compared with 13.7% for semaglutide. Similarly, waist circumference fell by 18.4 cm versus 13.0 cm.
Still, choosing between the two drugs is not just a matter of averages. It also depends on tolerability, underlying conditions, availability and cost. I discuss a real-world comparison in my article on Mounjaro or Wegovy and the SHAPE study.
What happens when you stop treatment?
The SURMOUNT-4 trial examined exactly this question. In the first phase, all participants received tirzepatide and lost an average of 20.9% of their body weight. Some then continued treatment, while others switched to placebo. Those who continued lost a further 5.5%. By contrast, those who stopped regained 14.0% of their weight. The conclusion is clear: obesity is a chronic disease, and its treatment is usually long-term.
Heart, liver and sleep: benefits beyond weight
Mounjaro (tirzepatide) and the heart
The SURPASS-CVOT trial compared the drug with dulaglutide, an established GLP-1 drug with proven cardiovascular protection. It enrolled 13,165 people with type 2 diabetes and heart disease. Over about four years of follow-up, the rate of heart attack, stroke and cardiovascular death was 8% lower (HR 0.92). This result showed that the drug is non-inferior, but it did not meet the threshold for superiority. In addition, death from any cause was 16% lower (HR 0.84).
What’s more, the SUMMIT trial enrolled 731 people with obesity and heart failure with preserved ejection fraction. Treatment reduced the risk of cardiovascular death or worsening heart failure by 38% (HR 0.62). You can read more in my article on Mounjaro and the heart.
Fatty liver and sleep apnea
The SYNERGY-NASH trial studied people with fatty liver inflammation (steatohepatitis) and fibrosis. After 52 weeks, the inflammation resolved in 44% to 62% of patients, depending on the dose, compared with only 10% in the placebo group. This was a phase 2 trial, so the results still await confirmation. I cover this in more detail in my article on Mounjaro for fatty liver.
In addition, the SURMOUNT-OSA trials studied people with obesity and obstructive sleep apnea. The number of breathing interruptions per hour fell by 25.3 and 29.3 events, compared with only 5.3 and 5.5 in the placebo groups. The FDA (the US Food and Drug Administration) has approved the drug for this indication as well.
Mounjaro (tirzepatide) dosing and administration
Mounjaro is given as a subcutaneous injection once a week, at any time of day, with or without food. You inject it into the abdomen, thigh or upper arm. Treatment starts at 2.5 mg per week for four weeks. Then the dose rises gradually, by 2.5 mg at a time, with at least four weeks at each step. Finally, maintenance doses are 5, 10 or 15 mg per week, depending on response and tolerability.
However, there is no need to reach the maximum dose. The right dose is the one that gives good control of hunger, weight loss and good tolerability. I discuss this principle in my article on whether every patient needs the maximum dose.
Side effects and safety
Most side effects involve the digestive system. The most common are nausea, diarrhea, constipation, vomiting and reduced appetite. They are usually mild to moderate and appear mainly after a dose increase, fading over time. To ease them, it helps to eat small portions slowly, cut back on fatty foods and drink enough fluids.
Rare risks include pancreatitis and gallstones, so severe or persistent abdominal pain calls for prompt medical evaluation. Anyone with a personal or family history of medullary thyroid cancer or MEN 2 syndrome must not use the drug. Also, do not combine it with another drug from the GLP-1 family. You’ll find a complete guide in my article on Mounjaro side effects.
Pregnancy and birth control pills
Women should not use Mounjaro during pregnancy. If you are planning a pregnancy, or become pregnant, stop treatment and consult your doctor. The drug may also reduce the absorption of birth control pills. Women taking the pill should therefore add a backup method, such as condoms, for four weeks after starting treatment. The same applies for four weeks after each dose increase.
Mounjaro in Israel: availability and coverage
Mounjaro is registered in Israel for the treatment of obesity and type 2 diabetes. However, the 2026 national health basket included a weight-loss injection for adolescents only, and Mounjaro was not included for adults. As a result, obesity treatment is either self-funded or partly covered by the supplementary insurance plans of Israel’s health funds (HMOs). Clalit, for example, added Mounjaro to its supplementary insurance in December 2025. I describe the arrangements at the different health funds in my article on Mounjaro and Israel’s health funds.
A holistic approach to treatment
For the best results, the treatment should be combined with a comprehensive lifestyle change program. This includes nutritional counseling and adequate protein intake, along with strength training, regular physical activity and good sleep. Together, these help preserve muscle mass during weight loss. This holistic approach turns weight loss into a lasting improvement in health.
How does Mounjaro work, and what does it do in the body? Watch the following video:
The bottom line on Mounjaro (tirzepatide)
Mounjaro (tirzepatide) is one of the most effective obesity medications available today. At the highest dose, it leads to an average loss of about one fifth of body weight. Beyond that, it improves blood sugar control, liver health and sleep apnea, and it has shown protective benefits in people with heart disease and heart failure. Even so, long-term success depends on persistence, medical follow-up and changes in habits.
The information in this article is general and does not replace personalized medical advice. Therefore, make any decision about drug treatment with a doctor who knows your medical history.
Frequently asked questions about Mounjaro (tirzepatide)
What is Mounjaro and how does it work?
It is a once-weekly injection based on tirzepatide. It acts on the receptors for the satiety hormones GIP and GLP-1, reducing hunger, slowing stomach emptying and improving blood sugar control.
Who is Mounjaro suitable for?
It is suitable for adults with a BMI over 30, and for those with a BMI over 27 who have related conditions such as diabetes, high blood pressure or fatty liver. Your doctor determines suitability after a full medical evaluation.
How much weight can you lose with Mounjaro?
In the SURMOUNT-1 trial, average weight loss ranged from 15.0% to 20.9%, depending on the dose. In people with diabetes, weight loss was more modest, at 12.8% to 14.7%.
When do you start to see results?
Some patients notice reduced appetite within the first few weeks. Overall, weight loss happens gradually over months, and it also depends on persistence and changes in habits.
Is it a lifelong treatment?
Obesity is a chronic disease. So, much like the treatment of high blood pressure or diabetes, long-term treatment is sometimes needed. In the SURMOUNT-4 trial, those who stopped the drug regained a large part of the weight they had lost.
What are the common side effects?
The most common are nausea, a feeling of fullness, diarrhea, constipation and sometimes vomiting. In most cases they are mild and pass, especially when the dose goes up gradually.
Safety, comparisons and sticking with treatment
Are there significant risks?
Rare risks include pancreatitis and gallstones, mainly as a result of rapid weight loss. That’s why regular medical follow-up throughout treatment is important.
Is Mounjaro better than Ozempic or Wegovy?
In the head-to-head comparison, Mounjaro led to greater weight loss. However, the choice depends on the patient’s profile, tolerability, underlying conditions and personal considerations. For information on a pill alternative, see the page on Foundayo.
Do I have to add exercise?
The drug is effective on its own. However, patients achieve the best and most lasting results when they combine it with a healthy diet, strength training and behavioral change.
What if the treatment stops working?
Sometimes a dose adjustment, a switch to another drug or a stronger focus on lifestyle is needed. This is a dynamic process that requires medical guidance. I write about new options in my article on CagriSema vs. tirzepatide.
References
Tirzepatide Once Weekly for the Treatment of Obesity
Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2)
Tirzepatide as Compared with Semaglutide for the Treatment of Obesity
SURPASS-CVOT: Is Tirzepatide Superior to Dulaglutide in Patients With T2D and ASCVD?
Tirzepatide for Heart Failure with Preserved Ejection Fraction and Obesity
Tirzepatide for Metabolic Dysfunction-Associated Steatohepatitis with Liver Fibrosis
Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity
After Maariv’s report: the new weight-loss drug available at Clalit from Sunday (Maariv, in Hebrew)
Eli Lilly, the drug’s manufacturer, funded the trials cited.
