How Does Mounjaro Work for Weight Loss?

Mounjaro and Zepbound are the same drug

Tirzepatide is sold under two names. Mounjaro was approved by the FDA in 2022 to treat type 2 diabetes. Zepbound, approved in 2023, is the same medication for long-term weight management in adults with obesity, or with overweight and a weight-related condition. In 2024 Zepbound was also approved for moderate to severe obstructive sleep apnea in adults with obesity. When Mounjaro is prescribed for weight loss in someone without diabetes, that is an off-label use.

How it works

After you eat, the gut releases hormones that tell the body food has arrived. Tirzepatide mimics two of them:

• GLP-1 (glucagon-like peptide-1)
• GIP (glucose-dependent insulinotropic polypeptide)

Semaglutide, the medication in Ozempic and Wegovy, acts on GLP-1 alone. Acting on both receptors produces several effects:

• Less hunger. It acts on appetite centers in the brain. People feel full sooner and think about food less.
• Slower stomach emptying. Food stays in the stomach longer, which extends fullness. This effect is strongest in the first weeks.
• Better blood sugar control. It increases insulin release when blood sugar is high and lowers glucagon, the hormone that raises blood sugar.
• Improved insulin sensitivity, partly through weight loss and possibly through GIP's effects on fat tissue.

The weight loss comes mainly from eating less.

What the trials found

• SURMOUNT-1 (about 2,500 adults with obesity, no diabetes): average weight loss of 15% to 20.9% of body weight at 72 weeks, depending on the dose, compared with 3.1% on placebo. All groups also received diet and activity counseling.
• SURMOUNT-5 (a head-to-head trial): tirzepatide produced an average loss of about 20%, compared with about 14% for semaglutide, at 72 weeks.
• SURPASS trials (type 2 diabetes): A1c fell by roughly 2 percentage points on average.
• Blood pressure, triglycerides and liver fat also improved.

These are averages. Some people lose more and some lose much less.

How it is taken

Tirzepatide is injected under the skin once a week, in the abdomen, thigh or upper arm. Treatment starts at a low amount and is increased step by step, no faster than every four weeks, to limit stomach side effects. The provider decides how far to increase based on response and tolerance. Many people do well below the maximum.

Side effects

Common, usually worst after each increase: nausea, diarrhea, vomiting, constipation, indigestion, reduced appetite and stomach pain. Smaller meals, less fat and enough fluid help.

Less common and more serious:

• Inflammation of the pancreas (pancreatitis). Severe abdominal pain that does not ease needs urgent care.
• Gallbladder problems, including gallstones.
• Low blood sugar, mainly when combined with insulin or sulfonylurea medications.
• Dehydration from vomiting or diarrhea, which can injure the kidneys.
• Worsening of diabetic eye disease in people with diabetes.
• Severe stomach problems.

Boxed warning. Tirzepatide caused thyroid C-cell tumors in rats. It is not known whether it does so in people. It must not be used by anyone with a personal or family history of medullary thyroid cancer or of multiple endocrine neoplasia syndrome type 2.

Other things to know

• Birth control pills. Tirzepatide can reduce the effectiveness of oral contraceptives. A backup method is advised for four weeks after starting and after each increase.
• Pregnancy and breastfeeding. Not recommended. Tell your provider if you are planning a pregnancy.
• Surgery and procedures. Because the stomach empties more slowly, tell the anesthesia team you take it.
• Muscle. Some of the weight lost is lean tissue. Protein and resistance training help preserve it.
• Stopping. In the SURMOUNT-4 trial, people who stopped tirzepatide regained a substantial part of the weight within a year, while those who continued kept it off. Obesity is treated as a long-term condition.

Who it is for

Under the FDA label for weight management, tirzepatide is for adults with a body mass index of 30 or higher, or 27 or higher with a weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol or sleep apnea. It is used together with changes in eating and activity.

How our program works

Our weight-loss programs are physician-led. A licensed provider reviews your health history and lab work and decides whether a medication is appropriate and which one. Increases are gradual. Check-ins are monthly, with messaging in between, and nutrition guidance is included. We serve all of New York & New Jersey, and our medical director oversees every treatment.

Quick answers

Is Mounjaro the same as Zepbound? Yes. Both are tirzepatide. Mounjaro is approved for type 2 diabetes and Zepbound for weight management and sleep apnea.

How is it different from Ozempic or Wegovy? Those contain semaglutide, which acts on GLP-1 only. Tirzepatide acts on GLP-1 and GIP.

How much weight do people lose? In the main trial, an average of 15% to 21% of body weight over about 16 months.

How fast does it work? Appetite usually falls in the first weeks. Weight loss continues for a year or more.

What are the most common side effects? Nausea, diarrhea, vomiting and constipation, mostly after each increase.

Who should not take it? Anyone with a personal or family history of medullary thyroid cancer or MEN 2, and anyone who is pregnant.

Do I have to take it forever? Weight tends to return after stopping. The plan for the long term is made with your provider.

Want to know if you qualify? See our weight-loss programs at zenivspa.com/glp/.

All treatments are medical services. Every guest is screened, and every treatment is provided only under the clearance, prescription or standing protocol of a licensed medical provider. Compounded peptides are not FDA-approved unless stated. Nothing on this page is a diagnosis or a promise of results.