Mounjaro for Weight Loss: How It Works, Side Effects & More

Craig Primack, MD, FACP, FAAP, FOMA

Reviewed by Craig Primack, MD, FACP, FAAP, FOMA

Written by Vanessa Gibbs

Published 04/05/2024

Trying to lose weight can be confusing, with so many different tips and diets out there. And that’s even before you throw in weight loss drugs like Mounjaro®, Ozempic® and Zepound® — just to name a few.

To make things a little less confusing, we’re here with all the info you need about popular weight loss med Mounjaro.

The TL;DR here is that Mounjaro is a diabetes drug that’s prescribed “off-label” for weight loss. It can help those who are overweight or have obesity lose significant amounts of weight, but it’s not without its risks and side effects.

Below, we cover everything you need to know about Mounjaro, including how it works, dosage and side effects.

Mounjaro, which is one brand name for the drug tirzepatide, is approved by the U.S. Food and Drug Administration (FDA) as a diabetes drug. It’s also sometimes prescribed off-label for weight loss.

When it comes to weight loss, Mounjaro can help those with and without type 2 diabetes lose weight.

Doses of 5 milligrams (mg) to 15mg of tirzepatide can help those with type 2 diabetes lose up to 15 percent of their body weight, and those without type 2 diabetes lose up to 21 percent of their body weight.

Is Mounjaro approved for weight loss? Nope. It’s FDA-approved as a diabetes drug to help people with type 2 diabetes better manage their blood sugar levels.

However, it can help people lose weight. That’s why It’s also prescribed “off-label” for weight loss, which is when a drug is prescribed for something that it isn’t approved for.

One thing to know is that another drug called Zepbound contains the same active ingredient as Mounjaro — tirzepatide — and is FDA-approved for weight loss.

Mounjaro is prescribed for those with type 2 diabetes who need medication to help manage their blood sugar.

For weight loss, Mounjaro may be prescribed off-label for those with a body mass index (BMI) of 30 or more or 27 or more with at least one weight-related condition, such as high blood pressure, type 2 diabetes, obstructive sleep apnea or cardiovascular disease.

There are a few groups of people who can’t take Mounjaro.

First, anyone who has a family history of medullary thyroid carcinoma or who has multiple endocrine neoplasia syndrome type 2 shouldn’t take Mounjaro.

Anyone who’s had a severe allergic reaction to tirzepatide or any of the inactive substances in Mounjaro should also avoid the drug.

Inactive substances in Mounjaro include:

  • Sodium chloride

  • Sodium phosphate dibasic heptahydrate

  • Hydrochloric acid solution

  • Sodium hydroxide solution

Also, let your healthcare provider know if you’re on oral birth control pills before taking Mounjaro. Mounjaro may not work as well if you’re taking oral birth control pills, so your provider may recommend a different type of birth control during your first four weeks on Mounjaro and for four weeks after every dose increase.

Mounjaro works for weight loss in a few different ways.

The drug’s active ingredient, tirzepatide, is a glucose-dependent insulinotropic polypeptide (GIP) receptor agonist and a glucagon-like peptide-1 (GLP-1) receptor agonist.

In less-sciencey speak, Mounjaro mimics GIP and GLP-1, hormones secreted in the intestine.

These hormones can help you lose weight. GLP-1 can lead to reduced appetite and increased satiety (feeling full). GIP can have similar effects — it can increase lipolysis, which is the breakdown of fats for energy, among other things.

In short, taking Mounjaro might make you feel less hungry, leading to you eating fewer calories and losing weight.

Other weight loss drugs, like Ozempic and Wegovy®, also have a GLP-1 receptor agonist that helps you lose weight as their active ingredient — semaglutide, in the case of these two medications. Tirzepatide may be more effective than semaglutide as it activates two hormone pathways, not just one.

A 2023 systematic review looked at 10 studies that included a total of almost 10,000 participants. It concluded that tirzepatide, in doses of 5mg, 10mg and 15mg, was more effective than other drugs in reducing body weight, including other GLP-1 receptor agonists.

You can dive deeper with our guide to Mounjaro vs. Ozempic.

In short, Mounjaro works, but there’s no guaranteed amount of Mounjaro weight loss. It may take several weeks for you to notice a difference, but reach out to your prescribing doctor if you’re not losing weight on Mounjaro after those first few weeks.

Technically, there isn’t a usual dosage of Mounjaro for weight loss, as it’s only approved as a diabetes drug. However, based on the dosage schedule for Zepbound, here’s what a Mounjaro dosage would likely look like:

  • A healthcare provider will get you started on a weekly dose of 2.5mg.

  • After four weeks, you’ll increase this to a 5mg weekly dose.

  • If needed, your dose could increase in 2.5mg increments, up to a maximum dose of 15mg. You’ll spend four weeks on each dose before increasing it again.

If you can tolerate the higher doses of Mounjaro, they seem to be more effective for weight loss.

A 2022 study with more than 2,500 participants looked at the effects of tirzepatide. These participants had a BMI of 30 or more or a BMI of 27 or more with one weight-related health condition that wasn’t diabetes.

They took a once-weekly injection of 5mg, 10mg or 15mg of tirzepatide or a placebo for 72 weeks. That included 20 weeks to increase the dose slowly.

At the end of the experiment, the average percentage change in weight was:

  • 15 percent for those taking 5mg of tirzepatide

  • 19.5 percent for those taking 10mg of tirzepatide

  • 20.9 percent for those taking 15mg of tirzepatide

  • 3.1 percent for those on the placebo

So, the higher the dose of Mounjaro you take, the better your weight loss results may be. A healthcare provider can work with you to find your best Mounjaro dose for weight loss and tell you when to increase your dose.

The common side effects of Mounjaro include:

  • Nausea

  • Vomiting

  • Diarrhea

  • Constipation

  • Abdominal pain

  • Dyspepsia (indigestion)

  • Decreased appetite — you’re probably looking for this one if you’re taking Mounjaro for weight loss

These side effects were reported by five percent or more of patients in clinical trials. They were also dose-dependent, meaning higher doses come with a higher risk of some side effects.

Serious Mounjaro Side Effects

There are a few more serious side effects to watch out for, although more research into Mounjaro's long-term side effects is needed.

Potential serious side effects of Mounjaro include:

  • Pancreatitis (inflammation of the pancreas)

  • Hypoglycemia (low blood sugar), when used with insulin secretagogues or insulin

  • Hypersensitivity reactions

  • Acute kidney injury

  • Severe gastrointestinal disease

  • Diabetic retinopathy complications in those with a history of this eye disease

  • Acute gallbladder disease

Mounjaro also comes with a black box warning stating that tirzepatide causes thyroid C-cell tumors in rats. For now, it’s unclear whether tirzepatide causes these tumors in humans.

How Long Do Mounjaro Side Effects Last?

The more common Mounjaro side effects should last a few days.

A 2024 review looked into tirzepatide trials and concluded that while side effects were relatively common, they typically resolved by themselves within a few days. Phew.

Prescribed online

Weight loss treatment that puts you first

Mounjaro is a subcutaneous (under the skin) injection. You inject it into your upper arm, stomach or thigh once a week, rotating the injection site with each dose.

There’s no real best time of day to take Mounjaro. You can take the drug at any time of day, with or without meals.

If you take Mounjaro, you should also prioritize a nutritious meal plan and increased movement. What this looks like will depend on your individual needs, so your prescribing doctor can give you more advice on building healthy lifestyle habits.

What to Do If You Miss a Dose of Mounjaro?

If you miss a dose of Mounjaro, don’t panic. Administer the injection as soon as you remember, as long as it’s within four days of your usual injection day.

If it’s been more than four days, skip the missed dose and take your next dose on your usual injection day.

Mounjaro is a prescription drug. If you’re looking into Mounjaro for weight loss, your first step is to talk to a healthcare professional about weight loss medications.

They can determine whether Mounjaro — or another weight loss drug or treatment — is suitable for you and write you a prescription if appropriate.

A healthcare provider may recommend Zepound instead of Mounjaro, especially if you don’t have type 2 diabetes. It may come down to the availability of the drugs and whether you have any pre-existing health conditions.

Mounjaro isn’t usually covered by health insurance when taken for weight loss.

Costs can vary and can add up, especially because you may take Mounjaro for an extended period.

For a rough idea, Mounjaro can cost $1000 to $1100 per month without insurance.

If those figures gave you sticker shock, know there are more affordable weight loss treatments. For example, our comprehensive weight loss programs start at $79 per month.

More research is needed to know exactly what happens when you stop taking Mounjaro, as it’s still a relatively new drug.

You may notice an increased appetite since the drug no longer suppresses your hunger. In addition, any side effects you were experiencing may clear up.

You may also regain some of the weight you’ve lost on the drug, but more studies are needed on this front. Research shows people may regain two-thirds of the weight they lost one year after stopping semaglutide, but it’s not clear if the same would happen with tirzepatide.

Can I Stop Taking Mounjaro?

You shouldn’t suddenly stop taking Mounjaro without consulting a healthcare provider first. That doesn’t mean you must keep taking it if side effects are giving you trouble or if you want to stop for another reason. It just means you need to talk to a healthcare provider to get the best advice on how and when to stop taking Mounjaro if you want to quit.

If you experience a severe reaction, however, stop taking Mounjaro immediately and seek medical advice.

You should also stop taking Mounjaro immediately and seek medical advice if you have stomach pain that won’t go away, with or without vomiting. This could be a sign of pancreatitis.

Mounjaro is just one of your weight loss medication options.

You’ve got other weight loss injections, such as:

  • Zepbound (tirzepatide)

  • Ozempic (semaglutide)

  • Wegovy (semaglutide)

  • Saxenda® (liraglutide)

  • Victoza® (liraglutide)

There are also weight loss medications that don’t involve a needle, such as:

  • Rybelsus® (semaglutide)

  • Metformin

  • Contrave® (naltrexone-bupropion)

  • Qsymia® (phentermine-topiramate)

  • Xenical® (orlistat)

  • Topamax® (topiramate)

A healthcare provider can walk you through the pros and cons of each medication and help you decide which one may be most suitable for you.

No matter which you choose, you should use weight loss medications in conjunction with drug-free interventions like healthy eating plans, increased movement and behavior change tools. These are all crucial tools to help you on your weight loss journey.

Mounjaro can help people with type 2 diabetes or those who are overweight or have obesity lose weight. But is it for you?

Here’s the final recap:

  • Mounjaro isn’t FDA-approved for weight loss. It’s approved as a diabetes drug and prescribed off-label for weight loss. Zepbound has the same active ingredient and is FDA-approved for weight loss.

  • Gastrointestinal side effects are common. Expect GI issues like nausea, vomiting and diarrhea. The silver lining here is that side effects should clear up on their own within a few days.

  • Your dose will start low and slowly increase. Your prescribing doctor can give you all the details, but you might get started on a 2.5mg weekly dose and slowly bump that up to a max of 15mg.

One of the most important things to know? Mounjaro isn’t your only option if you’re looking into weight loss treatments. There are other injectables, weight loss pills and drug-free interventions to suit every kind of body and every kind of weight loss journey.

12 Sources

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  2. Zepbound Highlights of Prescribing Information. (n.d.).
  3. Jensen, T. L., Brønden, A., Karstoft, K., Sonne, D. P., & Christensen, M. B. (2024). The Body weight Reducing Effects of Tirzepatide in People with and without Type 2 Diabetes: A Review on Efficacy and Adverse Effects. Patient preference and adherence, 18, 373–382.
  4. Lilly's tirzepatide shows additional 21.1% weight loss after 12 weeks of intensive lifestyle intervention, for a total mean weight loss of 26.6% from study entry over 84 weeks. (2023).
  5. FDA Approves New Medication for Chronic Weight Management. (2023).
  6. Min, T., & Bain, S. C. (2021). The Role of Tirzepatide, Dual GIP and GLP-1 Receptor Agonist, in the Management of Type 2 Diabetes: The SURPASS Clinical Trials. Diabetes therapy : research, treatment and education of diabetes and related disorders, 12(1), 143–157.
  7. Ozempic Highlights of Prescribing Information. (n.d.).
  8. What is Zepbound? Does this new weight loss drug work better than Wegovy and Ozempic? Will it cut costs? (2023). UC Health.
  9. Lin, F., Yu, B., Ling, B., Lv, G., Shang, H., Zhao, X., Jie, X., Chen, J., & Li, Y. (2023). Weight loss efficiency and safety of tirzepatide: A Systematic review. PloS one, 18(5), e0285197.
  10. Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., Wharton, S., Connery, L., Alves, B., Kiyosue, A., Zhang, S., Liu, B., Bunck, M. C., Stefanski, A., & SURMOUNT-1 Investigators (2022). Tirzepatide Once Weekly for the Treatment of Obesity. The New England journal of medicine, 387(3), 205–216.
  11. Mounjaro Prices, Coupons & Savings Tips. (n.d.).
  12. Wilding, J. P. H., Batterham, R. L., Davies, M., Van Gaal, L. F., Kandler, K., Konakli, K., Lingvay, I., McGowan, B. M., Oral, T. K., Rosenstock, J., Wadden, T. A., Wharton, S., Yokote, K., Kushner, R. F., & STEP 1 Study Group (2022). Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes, obesity & metabolism, 24(8), 1553–1564.
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