By Dr. Asnat Raziel, specialist in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal
Mounjaro guide: what this drug is and how it works
This Mounjaro guide explains a weekly injection for obesity and type 2 diabetes. Its active ingredient is tirzepatide. It is the first drug that acts on two satiety hormones at once. In the large trials, patients lost about one fifth of their body weight on average.
Here I focus on the drug itself: how it works, what the trials found and who it is for. You will find the practical side of treatment in my article on how to begin treatment step by step. In addition, I cover coping with the injections in a separate article on managing the side effects.
How Mounjaro works in the body
After a meal, the gut releases two natural hormones. The first is GLP-1, which signals fullness to the brain and slows stomach emptying. The second is GIP, which improves insulin release and also affects fat tissue. Older drugs, such as Wegovy, act on GLP-1 alone.
In contrast, tirzepatide activates both receptors together. As a result, hunger drops, fullness comes sooner and blood sugar stabilizes. Moreover, many patients describe a quieting of food noise, meaning intrusive thoughts about food throughout the day. If you want to dig deeper into the molecule and its development history, see the encyclopedia entry on tirzepatide.
Dosing: a short Mounjaro guide
You inject the drug once a week, under the skin, with a prefilled pen. First, treatment starts at 2.5 mg for four weeks. After that, the dose rises gradually, in steps of 2.5 mg at least every four weeks. Overall, the maximum dose is 15 mg. This slow increase aims to reduce nausea and digestive symptoms.
What the trials found: the evidence behind this Mounjaro guide
The tirzepatide research program in obesity goes by the name SURMOUNT. The main trial, SURMOUNT-1, enrolled 2,539 adults with obesity and without diabetes. Participants received a weekly injection for 72 weeks, together with lifestyle counseling.
- At 5 mg: average weight loss of 15.0% of body weight.
- At 10 mg: average loss of 19.5%.
- At 15 mg: average loss of 20.9%.
- In the placebo group (dummy injection): a loss of only 3.1%.
Put simply, out of 100 patients on 15 mg, 57 lost 20% or more of their weight. In comparison, only 3 out of 100 in the placebo group reached that mark. In addition, the researchers saw improvements in blood pressure, blood fats and blood sugar.
A head-to-head comparison with Wegovy
The SURMOUNT-5 trial compared the two drugs directly in 751 adults with obesity. After 72 weeks, patients on tirzepatide lost 20.2% of their weight on average. By contrast, patients on semaglutide lost 13.7%. I explain the practical differences in my article on Mounjaro versus Wegovy.
Sleep apnea
The SURMOUNT-OSA trial studied patients with obesity and moderate to severe sleep apnea. In the group not using a breathing device, breathing pauses fell by 25.3 events per hour. By comparison, the drop in the placebo group was only 5.3 events. Based on this trial, the US FDA expanded the approval to include sleep apnea. In fact, this made it the first drug to receive approval for obstructive sleep apnea.
Who can receive Mounjaro?
In the United States, the FDA approved tirzepatide for type 2 diabetes in May 2022, under the name Mounjaro. Then, in November 2023, the agency approved it for obesity under the name Zepbound. In Israel, the drug carries the name Mounjaro for both diabetes and obesity.
For obesity, the usual indication covers adults with a BMI (body mass index) of 30 or more. It also suits people with a BMI of 27 or more who have a related condition, such as high blood pressure, prediabetes or sleep apnea. However, the decision is always personal and rests on a full medical assessment.
Who should be cautious
- People with a personal or family history of medullary thyroid cancer, or MEN2 syndrome.
- Women who are pregnant, or who are planning a pregnancy soon.
- Patients who have had pancreatitis, or who have a severe digestive disease.
- Women taking birth control pills: the drug may weaken their effect, mainly at the start of treatment and after each dose increase.
Side effects of Mounjaro
The common side effects affect the digestive system: nausea, diarrhea, constipation and vomiting. In most cases they are mild to moderate and appear mainly while the dose is rising. In SURMOUNT-1, between 4.3% and 7.1% of patients on the drug stopped it because of side effects, compared with 2.6% on placebo.
Beyond that, rapid weight loss also includes some loss of muscle mass. Therefore, I recommend protein at every meal and strength training throughout treatment. It is also worth remembering that stopping treatment usually leads to weight regain. So plan any stop in advance with your doctor.
Mounjaro in Israel: availability and cost
As of October 2026, Mounjaro is not part of Israel’s national health basket for adults with obesity. The latest basket committee added an obesity drug only for adolescents aged 12 to 18. In practice, patients buy it with a prescription, and sometimes receive partial coverage through supplementary insurance. Criteria vary from one health fund to another, and I have summarized them in a separate article on Mounjaro in the health funds.
I want to stress that the drug is one tool within a complete program. At our clinic, we combine it with nutritional support, physical activity and medical follow-up. You will find an overview of all the options on my page about drug treatment for obesity. More information on Mounjaro for obesity appears in a separate article.
Bottom line of this Mounjaro guide
Mounjaro acts on two satiety hormones, so it leads to significant weight loss. In the trials, patients lost 15% to 21% of their weight on average, depending on the dose. However, this is a long-term drug that needs a personal plan and close follow-up. If you are considering treatment, consult a doctor who specializes in obesity, such as Dr. Asnat Raziel.
This article provides general information and is not personal medical advice. For any question about your treatment, please consult your doctor.
Mounjaro guide: questions and answers
What is the difference between Mounjaro and Zepbound?
There is no difference in the active ingredient. In other words, both contain tirzepatide. In the United States, Zepbound is the name for obesity treatment, while Israel uses the name Mounjaro for both indications.
How long does it take to see weight loss?
Most patients notice a drop in appetite within the first weeks. However, the full weight loss takes many months, and the trials measured it after 72 weeks.
Can I stop the injections once I reach my goal?
First of all, obesity is a chronic disease. For most patients, stopping treatment leads to the return of much of the weight. Therefore, make any decision to stop or lower the dose together with your doctor.
Is the drug also suitable for people with diabetes?
Yes. Regulators first approved tirzepatide for type 2 diabetes, and it improves both blood sugar control and weight.
References
Tirzepatide Once Weekly for the Treatment of Obesity
Tirzepatide as Compared with Semaglutide for the Treatment of Obesity
The 2026 health basket: obesity drugs are in, and what is out? (Globes, in Hebrew)
Tirzepatide for the Treatment of Obstructive Sleep Apnea and Obesity
