What are the side effects of Mounjaro and how to manage them?

Written by Prakrati Garg  ·  Reviewed by Sana Umar  ·  9 min read

Key takeaways

• Mounjaro (tirzepatide) is a once-weekly injectable GIP/GLP-1 dual agonist approved in India for obesity and type 2 diabetes.
• The most common side effects are gastrointestinal: nausea, diarrhoea, vomiting, constipation, indigestion, and abdominal pain.
• Most side effects occur during dose escalation and decrease over time with simple dietary adjustments.
• Rare but serious risks include pancreatitis, gallbladder disease, and hypersensitivity reactions — severe or persistent symptoms need urgent medical review.
• Mounjaro may reduce the efficacy of oral hormonal contraceptives; a non-oral or barrier method is advised for 4 weeks after each dose change.

Many a time, lifestyle and dietary changes alone are not sufficient to lose the desired weight, and one might require some support in their weight loss journey. At times, your doctor may introduce you to a weight-loss medication like Mounjaro, which contains tirzepatide as its active ingredient. (2)

Tirzepatide belongs to the drug class known as glucose-dependent insulinotropic polypeptide (GIP) receptor and glucagon-like peptide-1 (GLP-1) receptor agonists, and Mounjaro is a once-weekly injectable medicine. (2)

Although Mounjaro is primarily used to improve blood sugar control in adults with type 2 diabetes, tirzepatide has also shown meaningful weight-loss outcomes in clinical trials. (2)(3)

If you are considering using Mounjaro for weight loss, it is essential to know the common side effects of this treatment and how to navigate them. More importantly, if you have certain personal or family medical history, there are rare but serious risks that you should discuss with your clinician before starting. (2)

Mounjaro: How does it work for weight loss?

In India, Eli Lilly has launched Mounjaro for obesity and type 2 diabetes, following regulatory clearance. (1)

Mounjaro acts as a double agonist, which means it activates two receptors at once: GIP and GLP-1. By influencing incretin pathways, it can reduce appetite, change digestion (including slowing gastric emptying), and improve glucose regulation, which together can support weight loss for many people when used alongside lifestyle changes. (2)

In the SURMOUNT-1 trial (72 weeks, 2,539 participants with obesity/overweight without diabetes), average weight loss was about 20.9% with tirzepatide 15 mg compared with about 3.1% with placebo. In the same trial, 90.9% of participants on 15 mg achieved at least 5% weight loss, and 56.7% achieved at least 20% weight loss at week 72. (3)

A 2023 systematic review (10 randomised trials, 9,873 participants) also found tirzepatide produced significant weight reduction, with gastrointestinal side effects being the most common tolerability issue. (4)

Note: Some newer headlines mention semaglutide 7.2 mg showing around 20.7% average weight loss at 72 weeks, but this refers to an investigational higher dose highlighted in a company announcement and may not reflect routine clinical dosing everywhere. (5)

Some common side effects of Mounjaro

Just like most drugs, Mounjaro can cause side effects, and the most common ones are digestive. According to the prescribing information, the most common adverse reactions (reported in 5% or more of patients) are nausea, diarrhoea, decreased appetite, vomiting, constipation, dyspepsia (indigestion), and abdominal pain. (2)

Before starting Mounjaro, it is a good idea to speak with a trusted healthcare advisor and discuss your health history and current medications, so you can start with a plan that prioritises safety and tolerability. (2)

Nausea

Nausea is among the most frequently reported side effects of Mounjaro. It is often more noticeable when you start treatment or when your dose is increased. (2)

Diarrhoea

Diarrhoea is another common side effect in clinical studies. It may be linked to changes in digestion and gut signalling while your body adjusts to the medication. (2)

Decreased appetite

Decreased appetite is a key effect of Mounjaro and one reason people may lose weight on it. At the same time, a sharp appetite drop can make it easier to under-eat protein or fluids, so it helps to stay intentional with meals. (2)

Vomiting

Vomiting can happen, particularly early on or around dose escalation, and it often comes alongside nausea. If vomiting persists, it is worth speaking to your prescriber early to avoid dehydration and to review whether dose escalation needs to be slowed. (2)

Constipation

Constipation is also reported with Mounjaro in clinical trials. Lower food volume, slower gut movement, and low fluid intake can all contribute. (2)

Indigestion (dyspepsia)

If you are dealing with indigestion, heaviness, burping, or discomfort, you may be experiencing dyspepsia, which is listed among common adverse reactions. For many people, high-fat meals, alcohol, and large portions can make reflux or indigestion feel worse during the adjustment phase. (2)

Abdominal pain

Abdominal pain is another reported side effect. Mild discomfort may ease with time, but strong or persistent abdominal pain should not be brushed aside because the label includes important warnings related to pancreatitis and gallbladder disease. (2)

Mitigating the side effects

Most mild side effects from Mounjaro are manageable, and a few practical changes can make the first few weeks much more comfortable. A useful thing to remember is that many gastrointestinal side effects occur during dose escalation and often decrease over time. (2)

Here is what usually helps, without overcomplicating it:

• If nausea (or nausea-related vomiting) is bothering you: Try smaller meals, choose plain foods, avoid greasy or spicy meals for a while, and sip fluids through the day. (2)
• If diarrhoea shows up: Focus on hydration first (water and electrolytes if needed), and keep food simple until stools normalise. (2)
• If constipation is an issue: Increase water intake, add fibre gradually (fruits, vegetables, whole grains), and keep daily movement light but consistent. (2)
• If indigestion or heartburn is getting in the way: Cut back on heavy, high-fat meals, eat slower, and avoid late-night large portions. (2)

If symptoms feel intense, are not improving, or are affecting hydration and nutrition, talk to your prescriber sooner rather than later, because holding a dose longer (instead of escalating) is sometimes the simplest fix. (2)

Safety notes and FAQs

How long do the side effects last?

There is no single timeline, but the prescribing information notes that many reports of nausea, vomiting, and diarrhoea occurred during dose escalation and decreased over time. If anything feels unusual, severe, or persistent, checking in with your doctor is the safest approach. (2)

What to keep in mind before starting

• Missed dose guidance: If a dose is missed, the label advises taking it as soon as possible within 4 days (96 hours), otherwise skip it and take the next dose on the regularly scheduled day. (2)
• Low blood sugar risk: Hypoglycaemia risk increases when Mounjaro is used with insulin or sulfonylureas, and your clinician may need to adjust other diabetes medicines. (2)
• Serious symptoms that need urgent care: The label highlights risks including pancreatitis, gallbladder disease, and hypersensitivity reactions, so severe abdominal pain, facial or throat swelling, or breathing difficulty should be treated as urgent. (2)
• Thyroid warning: Mounjaro has a boxed warning about thyroid C-cell tumours observed in rats, and it is contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN2. (2)

Can Mounjaro interfere with contraceptives?

Yes, it can. Mounjaro delays gastric emptying and may reduce the efficacy of oral hormonal contraceptives, so the label advises switching to a non-oral method or adding a barrier method for 4 weeks after starting and for 4 weeks after each dose escalation. Australia's TGA has also published updated contraception advice consistent with this approach. (2)(6)

Is it possible to switch from Mounjaro to Wegovy?

Switching can be done, but these medicines are not interchangeable and should not be used at the same time, so timing and dose selection should be clinician-led. At Karespot, the focus is to make any switch structured and supported, based on your treatment history, tolerability, and progress.

References

1. Express Healthcare. Eli Lilly launches Mounjaro in India for obesity and type 2 diabetes. 19 Mar 2025. https://www.expresshealthcare.in/news/eli-lilly-launches-mounjaro-in-india-for-obesity-and-type-2-diabetes/448379/
2. U.S. FDA. Mounjaro (tirzepatide) prescribing information. 2022 and later updates. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/215866s000lbl.pdf
3. American College of Cardiology. SURMOUNT 1: Tirzepatide once weekly for the treatment of obesity. 2022. https://www.acc.org/Latest-in-Cardiology/Clinical-Trials/2022/08/04/15/32/SURMOUNT-1
4. PLOS ONE. Weight loss efficiency and safety of tirzepatide: A systematic review. 2023;18(5):e0285197. https://doi.org/10.1371/journal.pone.0285197
5. Novo Nordisk. Semaglutide 7.2 mg achieved 20.7% weight loss in the STEP UP obesity trial. 17 Jan 2025. https://www.globenewswire.com/news-release/2025/01/17/3011376/
6. Therapeutic Goods Administration Australia. Updated contraception advice for Mounjaro (tirzepatide). 30 Nov 2025. https://www.tga.gov.au/news/safety-updates/updated-contraception-advice-mounjaro-tirzepatide