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 or Wegovy: what happens outside controlled trials
“Mounjaro or Wegovy?” is one of the most common questions I hear in my clinic. The SHAPE study looked at this question in almost 10,000 Americans with overweight or obesity and without diabetes. After a year of continuous treatment, Wegovy patients lost an average of 14.6 kg, while tirzepatide patients lost 17.2 kg. The surprising finding: only about a quarter of tirzepatide patients reached the maximum dose.
The two medications in brief
Wegovy contains semaglutide at a dose of up to 2.4 mg a week. It acts on the hormone GLP-1, which increases fullness and reduces hunger. Mounjaro contains tirzepatide, which acts on two hormones: GLP-1 and GIP. Doctors raise its dose gradually from 2.5 mg up to 15 mg a week. In the United States, the same active ingredient is also sold for obesity under the name Zepbound. I wrote about how these drugs work in the brain in my article on GLP-1 medications and the brain.
What the SHAPE study examined
The SHAPE study was published in the journal Advances in Therapy. The researchers used Komodo Health, a US database that brings together insurance claims and medical records. They included adults with overweight or obesity, without type 2 diabetes, who started treatment between June 2021 and December 2023. For people with diabetes, see my article on real-world data in diabetes.
In addition, the researchers set an important condition: patients had to stay on treatment for a full year, with no break longer than 30 days. They also needed a weight measurement at the start of treatment and after one year. In total, the study included 9,916 patients: 6,794 took Wegovy and 3,122 took tirzepatide.
Who the patients were
Overall, the two groups were very similar. The average age was 47.8 in the Wegovy group and 49.5 in the tirzepatide group. Most patients were women: 79.8% and 77.9%, respectively. Average starting weight was 104.5 kg and 104.9 kg.
Mounjaro or Wegovy: the results after one year
These are the study’s key findings:
- Wegovy: an average loss of 14.6 kg, or 14.1% of body weight.
- Tirzepatide: an average loss of 17.2 kg, or 16.5% of body weight.
- 84.1% of Wegovy patients lost at least 5% of their weight, compared with 86.2% of tirzepatide patients.
In other words, a person weighing 105 kg dropped on average to about 90 kg with Wegovy, and to about 88 kg with tirzepatide. In both groups, this is a medically meaningful loss. Even losing 5% to 10% of your weight already improves blood pressure, blood sugar and blood fats. I looked at those changes in my article on Wegovy and metabolic health after one year.
Mounjaro or Wegovy: the surprising dose finding
Here is the most interesting part of the study. First, 83.5% of Wegovy patients reached the maximum dose of 2.4 mg. By contrast, only 25.9% of tirzepatide patients reached the maximum dose of 15 mg. The rest stayed on lower doses: 19.6% reached 7.5 mg, 20.8% reached 10 mg and 19.1% reached 12.5 mg.
In other words, tirzepatide produced substantial weight loss even though most patients never reached its highest dose. The researchers did not look into the reasons. Perhaps some patients already responded well to a moderate dose, or perhaps availability or cost got in the way. I wrote about when it makes sense to raise the dose in my article should you increase your tirzepatide or semaglutide dose?
Mounjaro or Wegovy: why not to read too much into it
It is important to understand the study’s limits. First, this is a descriptive study. The researchers did not run a statistical comparison between the groups, so we cannot say the difference is significant. Second, the study included only people who stayed on treatment for a full year and were weighed at the end. In reality, many patients stop early, so the average in the general population is likely to be lower.
Third, most tirzepatide patients received Mounjaro, which in the US is approved only for diabetes, rather than Zepbound. That means they were taking the drug off-label for obesity. Also, insurance data may contain recording errors. Finally, the study was funded by Novo Nordisk, the maker of Wegovy, and all the researchers are company employees. Even so, this very study showed substantial weight loss with the competing drug.
How this fits with controlled trials
The findings are consistent with the SURMOUNT-5 trial, a direct, controlled head-to-head comparison of the two drugs. In that trial, tirzepatide led to greater weight loss than semaglutide. I wrote about that trial and the high-dose comparison in my article on Mounjaro vs. Wegovy at high doses. In addition, researchers have recently tested Wegovy at a high dose of 7.2 mg, as I described in my article on Wegovy 7.2 mg.
Mounjaro or Wegovy: how to choose
Of course, no single medication suits everyone. The choice depends on your other medical conditions, any heart or liver disease, side effects, availability and cost. For example, a patient with existing heart disease may prefer a drug with a specific approval in that area. On the other hand, a patient whose main goal is a large weight loss may prefer a different drug.
A few practical principles for anyone starting treatment:
- Persistence is key. Each drug’s benefit shows up only when you take it over time.
- Rapid weight loss can come at the expense of muscle. That’s why it’s important to eat enough protein and exercise. I wrote about this in my article on GLP-1 medications and muscle.
- A tailored diet reduces nausea and keeps your energy up. I recommend reading my guide to eating well on weight-loss injections.
- Stopping treatment usually leads to weight regain, so it’s worth planning ahead.
Bottom line
In the SHAPE study, people without diabetes who stayed on treatment for a year lost an average of 14.6 kg with Wegovy and 17.2 kg with tirzepatide. Interestingly, the loss with tirzepatide came even though only 25.9% of patients reached the maximum dose. Ultimately, the question “Mounjaro or Wegovy” is not about a winning drug but about finding the right fit for each patient.
The information in this article is general information only and is not a substitute for personal medical advice. Before starting or changing any treatment, consult your doctor.
References
Tirzepatide as Compared with Semaglutide for the Treatment of Obesity
The SHAPE study was funded by Novo Nordisk, and all the researchers are employees and shareholders of the company.
