December 9, 2023

Less than a year ago, many people had never heard of the diabetes medication Mounjaro. But that has quickly changed as the drug has grabbed countless headlines as one of the most effective weight loss drugs available.

Woman doing insulin injection

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“Newer medicines are needed because the number of patients who are overweight and obese continue to increase, and this is associated with greater severity of health complications,” says Dr. Reshmi Srinath, associate professor and director of weight and metabolism management program at the Icahn School of Medicine at Mount Sinai in New York City. “Some of the drugs we have can help lose about 10% of body weight, but the next generation drugs like tirzepatide give clinicians much better tools to help people with obesity lose weight.”

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What Is Mounjaro?

Mounjaro, chemically known as tirzepatide, is an injectable medication that was approved by the FDA in 2022 to treat Type 2 diabetes.

Although the drug is not currently approved for weight loss, it is being used off-label for that purpose. In clinical trials, people with obesity taking Mounjaro lost around 20% or more of their body weight within a year and a half of starting treatment. The FDA is expected to approve the drug for weight loss before the end of the year. However, the drug will be given a different brand name than Mounjaro upon approval, according to industry insiders.

How Does Mounjaro Work?

Tirzepatide uniquely activates two receptors simultaneously, which is why it’s called a dual-targeted or dual-agonist medicine. This dual-action stimulates two hormones: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors. While its exact mechanism is unclear, tirzepatide targets the appetite centers of the brain that initiate a feeling of fullness.

“This agent is part of a completely new class of drugs,” says Dr. Cecilia Low Wang, an endocrinologist with UCHealth and professor of medicine at the University of Colorado School of Medicine in Aurora, Colorado. “Its dual action not only promotes the release of insulin to help improve glucose control, but leads people to eat less, feel fuller and, therefore, lose weight.”

Dosage for Mounjaro

As a treatment for Type 2 diabetes, the starting dosage of Mounjaro is 2.5 milligrams, taken weekly. Typically, people start a dosage of 2.5 milligrams to allow the body to get used to the medication. After four weeks, it’s increased in increments of 2.5 milligrams until an effective dosage is reached. The maximum dosage is 15 milligrams weekly. Each pen of Mounjaro contains a single dose of the medication in a liquid solution. You use the pen to inject the solution under the skin of your upper arm, abdomen or thigh.

“We start patients on a low dose for four weeks, then increase the dose and that seems to help with tolerability,” Low Wang explains.

How Much Weight Can You Lose?

Tirzepatide has been clinically shown to help people lose 15% to over 26% of their body weight, depending on the dosage.

The SURMOUNT-3 and SURMOUNT-4 trials conducted by Eli Lilly, the manufacturer of Mounjaro, found that when taking tirzepatide, patients with obesity experienced 26.6% weight loss over the course of 84 weeks. Patients on the SURMOUNT-3 trial also underwent an intensive lifestyle intervention that included a low calorie diet, exercise, and weekly counseling sessions.

In another major study, published in the New England Journal of Medicine, tirzepatide was evaluated in adults with obesity and at least one weight-related comorbidity, excluding diabetes. The trial included more than 2,500 adults with a mean body weight of 230 pounds who were randomly assigned to receive either a weekly subcutaneous injection of 5, 10 or 15 milligrams of tirzepatide or placebo for 72 weeks. Participants were provided counseling to reduce caloric intake by 500 calories a day and were directed to exercise 150 minutes per week.

At the end of the study, the average decrease in weight was 15% for those taking a 5 milligram dose, 19.5% for those taking a 10 milligram dose and 20.9% for those taking a 15 milligram dose. Comparatively, the average decrease in weight in the placebo group was 3.1%. There were also improved cardiovascular and metabolic measures found in those taking tirzepatide.

What this means is that for someone who weighs about 200 pounds, they will lose on average about 28 pounds on tirzepatide, Srinath says.

“These findings open up promising new options not only for Type 2 diabetes management, but also offering the potential dual benefit of blood sugar control and weight management,” Srinath adds.

While weight typically comes off quickly during the initial phase, people may experience weight loss plateaus, a period in which weight loss begins to stall. For some people, the plateau may last a short period of time, while it may last longer for others. That’s why it’s important to make sure that you combine these types of medications with healthful eating and regular exercise. Fine-tuning and tweaking your healthy lifestyle habits can give your weight loss the boost it needs to break out of the plateau.

What Are the Side Effects of Mounjaro?

Common side effects of Mounjaro include:

Other serious side effects may include:

Doctors advise against prescribing the drug for people with severe stomach problems. In rare cases, the stomach takes too long to empty and leads to gastroparesis, a condition characterized by stomach paralysis.
In clinical studies, adverse events caused treatment discontinuation in 4.3%, 7.1%, 6.2%, and 2.6% of participants receiving 5, 10 and 15 milligram tirzepatide doses and placebo, respectively.

“It’s a low percentage of people who have side effects. The majority of people tolerate this medication very well,” Low Wang says.

While studies show that tirzepatide is safe overall, the long-term effects are still unknown.

As with other popular diabetes drugs used for weight loss, one of the side effects of stopping Mounjaro may include regaining weight. To avoid rebound weight gain, it’s important to maintain a healthy lifestyle that includes eating a nutritious, well-balanced diet and incorporating regular physical activity into your daily routine.

What’s the Difference Between Mounjaro, Ozempic and Wegovy?

There are several brands of weight loss drugs available, so it’s important to know the difference.

While Mounjaro is a dual GIP/GLP-1 agonist, Ozempic and Wegovy are both GLP-1 agonists, known chemically as semaglutide, that are currently approved to treat Type 2 diabetes and weight loss, respectively.

But how does Mounjaro stack up against Ozempic and Wegovy in helping people lose weight? In a 2023 study, tirzepatide was shown to be more effective in promoting weight loss compared with semaglutide, with those taking tirzepatide losing 5.4% more than the other group. Furthermore, according to FDA regulators, the average weight loss with 15 milligrams of tirzepatide resulted in patients losing 12 pounds more on average than those who used semaglutide in a diabetes study.

A major head-to-head study examining tirzepatide against semaglutide was announced earlier this year with the goal of enrolling about 700 non-diabetic adult participants who have obesity or are overweight with weight-related comorbidities. The study is expected to be completed in early 2025.

Will Health Insurance Cover Mounjaro?

Commercial health insurers have generally been covering Mounjaro for the treatment of Type 2 diabetes. According to Lilly, the list price of Mounjaro for diabetes is $1,023.04 per fill, which consists of four pens per month. However, for those interested in Mounjaro to lose weight, it’s important to note that the drug is not FDA-approved for weight loss and, therefore, is not covered by health insurance plans for non-diabetes purposes.

While that may change once the FDA officially approves the drug as a weight loss treatment, insurers are expected to put restrictions in place to curb widespread use. Medicare coverage of drugs for weight has been scarce except under certain medical situations.

Bottom Line

The scientific community is continuing to explore effective weight loss management solutions. Researchers are looking into developing other dual-agonists that have the potential to help people lose even more weight, as well as other ways of delivering the drug. For example, pharmaceutical companies are developing drugs in pill forms versus subcutaneous injections.

“In a world where obesity and its associated health risks loom large, medical advancements like tirzepatide and other weight loss medications offer hope for those striving to shed excess weight and lead healthier lives,” Srinath says.

If you have Type 2 diabetes and are overweight or have obesity, talk with your health care provider to see if Mounjaro is right for you.


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