Does Mounjaro work? What you need to know about Mounjaro for weight loss

Since May 2022, when the U.S. Food and Drug Administration (FDA) approved it as a treatment for type 2 diabetes, Eli Lilly’s Mounjaro® has generated widespread interest for its ability in clinical trials to support weight loss.

In 2023, the FDA approved tirzepatide, the active ingredient in Mounjaro, as an obesity treatment under the brand name Zepbound®, which is also manufactured by Eli Lilly. Tirzepatide is the first medication in its class to win approval for weight loss and the only medication to demonstrate results comparable to bariatric surgery.

So how does Mounjaro work, and could it be a good choice for you? 

How does Mounjaro work to cause weight loss? 

Mounjaro can be highly effective for weight loss because it targets two hormone receptors. The first, glucagon-like peptide-1 (GLP-1) receptors are the same receptors that other diabetes medications like semaglutide (the active ingredient in Ozempic® and Wegovy®) trigger. Activating the GLP-1 receptor increases insulin secretion while reducing glucagon and helps lower blood sugar levels. These drugs also slow gastric emptying, so you feel full longer and activate GLP-1 receptors in your brain that tamp down appetite, so you don’t get hungry again as soon after eating. 

Mounjaro also activates the GIP receptor. (Researchers have long believed that the GIP hormone is associated with obesity.) Levels of GIP secretion are typically higher in people with obesity, and higher levels of this hormone can prompt the body to create more fatty tissue. 

However, drugs that trigger GIP receptor cells, like Mounjaro, support more weight loss than medications that only trigger the GLP-1 receptors. While researchers are still studying the exact mechanism of why Mounjaro works so well for weight loss, they believe one of its effects is that the medication lasts longer in the body than the natural GIP hormone. This long-lasting activation of the GIP hormone signals your brain that you feel full, decreasing your food intake. There’s also evidence that the GIP receptor agonist enhances how your body uses energy, increasing your metabolism and resulting in more weight loss when combined with a GLP-1 receptor agonist. 

Is Mounjaro better than Ozempic or Wegovy? 

Both Ozempic and Wegovy have the same active ingredient, semaglutide. Semaglutide is a GLP-1 agonist meaning it only activates the GLP-1 receptor instead of GLP-1 and GIP receptors like Mounjaro. 

In clinical trials, semaglutide is very effective for weight loss. In a meta-analysis of randomized controlled clinical trials, patients without type 2 diabetes who took a weekly dose of 2.4 mg of semaglutide (the maximum dose for weight loss) lost an average of 12.1% of their initial body weight. 

However, a similar analysis of clinical trials of tirzepatide found that the weekly maximum dose (15 mg) for the dual agonist resulted in an average weight loss of 20.9% of body weight. In a 40-week study comparing the effectiveness of tirzepatide with semaglutide for people with diabetes, patients who took tirzepatide lost an average of 12 more pounds than those taking semaglutide. 

But clinical averages can’t give you the complete picture of how a medication will work for you. When deciding which weight loss medication is best for you, it’s essential to consider the full picture of your health history, goals, and even your insurance and budget. At Found Health, your prescribing health care provider evaluates your history, needs, and preferences to provide individualized weight care that helps you meet your goals in the way that’s best for you. 

How long does it take for Mounjaro to start working for weight loss? 

The starting dose for Mounjaro, as recommended by Eli Lilly, is 2.5 mg injected once weekly. Your provider may increase your dose every four weeks by 2.5 mg, depending on how well it’s working and whether you are experiencing any side effects. 

Taking the highest dose of Mounjaro results in the most significant weight average weight loss, and most people typically start to see results several weeks after starting Mounjaro. In one study, patients who took Mounjaro lost an average of 3.1% of their body weight during the first month of the trial. Another study found similar results: Those taking 5 mg of tirzepatide for 16 weeks lost at least 5%,  while those who took higher doses of tirzepatide (10 mg or 15 mg) lost 5% or more of body weight after only 12.4 weeks. 

Do you gain weight after stopping Mounjaro? 

Mounjaro is a highly effective medication for weight loss, but one potential downside is that you may need to continue taking it long-term. In one study, people who took tirzepatide for 36 weeks lost an average of 20.9% of body weight. But after 36 weeks, those who were switched to a placebo while continuing their lifestyle changes still regained about 14% of the weight they’d lost. That same study found those who continued taking tirzepatide lost an additional 5.5% of body weight at the end of 52 weeks. 

Since Mounjaro is a new medication, there aren’t yet many studies on whether other treatments or lifestyle changes can help people maintain weight goals after stopping tirzepatide. However, a study of liraglutide—a GLP-1 receptor agonist—found that a medically supervised exercise program with cardiovascular physical activity could help people maintain their new weight and BMI after stopping the medication. Researchers continue to study the best treatments for ongoing weight management, but it may be that continuing a maintenance dose of your medication is the best way to sustain your weight goals. 

What are the side effects of Mounjaro?  

GLP-1 and GLP-1/GIP medications like Mounjaro do have some known potential side effects. The most common side effects are nausea, vomiting, diarrhea, constipation, abdominal pain, decreased appetite, and indigestion. More serious but less common side effects include pancreatitis, gallbladder disease, and worsening of diabetic eye disease. Tirzepatide and GLP-1s can also cause hypoglycemia when combined with insulin. Those with a personal or family history of some health conditions, including medullary thyroid cancer or multiple endocrine neoplasias, should not use these drugs. Find detailed side effect and risk information for specific medications by name on our dedicated medication page.

About Found

Found is among the largest medically-supported telehealth weight care platforms in the country, having served more than 250,000 members to date. To discover your MetabolicPrint™ and start your journey with Found, take our quiz. 

Found is not affiliated with Eli Lilly and Co., the owner of the registered trademarks Mounjaro® and Zepbound®, nor is it affiliated with Novo Nordisk A/S., the owner of the registered trademarks Wegovy® and Ozempic®. The content provided is for informational purposes only and should not be used as a basis for diagnosing or treating any health condition. Always follow your healthcare provider’s instructions to ensure safe and effective management of your health conditions. Certain medications are only FDA approved to treat conditions other than weight but may be prescribed to help aid in weight loss. Prescriptions are up to a medical provider’s discretion. For key risk information by drug, visit the Found medication page.