Wegovy vs Mounjaro Side Effects: Similarities & Differences

If you’re thinking of using treatment to manage your weight, you’ve probably come across Eli Lilly’s Mounjaro (tirzepatide) and Novo Nordisk’s Wegovy (semaglutide). Both are weekly injectable treatments that have become increasingly popular for weight management.

For most patients, side effects play a major role in making a final decision. No one likes feeling ill, especially if you have a busy day-to-day life. So you might be wondering “which injection has the least side effects?”

The good news is that side effects on both treatments are usually mild and temporary. But what are the differences (and similarities) between side effects on Wegovy vs Mounjaro? Here, we compare the two.

How Wegovy and Mounjaro Work: Similarities and Differences

Both Wegovy and Mounjaro are weekly injections, where you increase your dose gradually over time. How quickly this increases will depend on your progress and how well you tolerate the treatment.

You inject them under the skin, in the lower abdomen, thighs, or back of the arms.

They both work by mimicking hormones that regulate appetite and help with blood sugar control. However, they are not identical. Wegovy acts on glucagon-like peptide-1 (GLP-1) hormone receptors. Mounjaro targets both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors.

This dual action, it is believed, allows Mounjaro to provide greater average weight loss results. In clinical trials, patients taking Mounjaro lost an average of 22.5% of their starting body weight after 68 weeks. Meanwhile, those on Wegovy lost around 17% after 72 weeks.

Common Wegovy vs Mounjaro Side Effects

“Side effects [of Wegovy] are often similar to those experienced on Mounjaro, with things like nausea or stomach upset,” says Chief Clinical Officer Abdal Alvi. “But if you tolerate Mounjaro well, you’ll likely manage Wegovy well too.”

Both medications work by suppressing appetite, helping you feel fuller for longer. This appetite-suppressing effect helps you lose weight, when combined with a healthy, balanced diet and exercise.

Because Wegovy and Mounjaro work similarly, their side effects are also quite similar. The most common side effects for both medications tend to be stomach related.

This is because both medications change how your body processes food. The appetite-suppressing effects can change what you’re eating, leading to reduced dietary fibre and water intake.

Very Common Side Effects
Mounjaro	Wegovy
Feeling Sick (Nausea)	Feeling Sick (Nausea)
Being Sick (Vomiting)	Being Sick (Vomiting)
Constipation	Constipation
Diarrhoea	Diarrhoea
Stomach Pain	Stomach Pain
	Feeling Weak or Tired
	Headache

Which Has Worse Side Effects, Wegovy or Mounjaro?

The side effects of Mounjaro and Wegovy are fairly similar. And there are no completely unique side effects that belong only to one treatment. The difference often comes down to how frequently or how severely patients experience them.

While both Mounjaro and Wegovy tend to cause similar side effects, some of these side effects can be more pronounced with Mounjaro.

The British National Formulary (BNF) notes that gallbladder-related problems, such as gallstones, are reported more frequently with Mounjaro than with Wegovy. Its stronger effects on weight loss can also make fatigue or stomach upset feel more intense.

Both medications carry a rare risk of inflammation of the pancreas (pancreatitis). And both include warnings about certain thyroid tumours observed in animal studies. Although studies have not confirmed it in humans.

Your prescriber will closely monitor your symptoms and tailor the dosing regime to best suit your personal needs.

Side Effects Differ From Person to Person

Not everyone experiences side effects in the same way. Some people may tolerate Wegovy better, while others respond better to Mounjaro.

Your medical history, other health conditions, medicines, and even genetic factors can all influence how your body reacts. Choosing between the two treatments is therefore not just about which is more effective, but also about how well you tolerate it.

Whichever option you choose to go with, your prescriber will adjust the dose and schedule to best suit your progress and response. Most patients feel side effects more when just starting treatment or moving up to a higher dose.

If you’re on one of these treatments and are considering switching, discuss this with your prescriber. In general, if you tolerated one treatment well, you are likely to tolerate the other in a similar way. If you need support, contact us on 0141 774 5023.

When to Seek Medical Help

Both Mounjaro and Wegovy are authorised medicines. They’re safe and effective when prescribed by a licensed clinician and purchased from a licensed pharmacy.

But there are rare serious side effects that require you to seek immediate medical attention, these include:

• Severe, persistent stomach pain (especially pain that spreads to the back) can be a sign of pancreatitis. This may be with or without vomiting. See a GP immediately or call NHS 111.
• Signs of a serious allergic reaction. Such as sudden swelling of the face, lips or throat, difficulty breathing, wheeze, or fainting. Call 999 straight away.
• Severe or prolonged vomiting and diarrhoea with inability to keep fluids down (risk of dehydration). Contact your prescriber or NHS 111.
• Symptoms of low blood sugar (hypoglycaemia) are more common if you also take insulin or other diabetes medications. Contact your GP immediately or call NHS 111.

If you have any worrying or persistent side effects, contact your prescriber or pharmacist for further guidance.

Key Takeaways

• Mounjaro and Wegovy Work in Similar Ways: Both weight loss injections belong to the GLP-1 receptor agonist class. But Mounjaro also targets the GIP receptor, giving it a dual mechanism of action.
• Side Effects of Mounjaro and Wegovy Are Similar: Because they both work in similar ways, patients experience similar side effects on both the medications. The most common ones include nausea, vomiting, constipation and diarrhoea.
• Mounjaro Shows Greater Average Weight Loss: In just over a year, patients on Mounjaro lose about 22.5% of body weight, compared to 17% with Wegovy. Individual results can vary.
• Side Effects Can Differ Between Patients: Both treatments share common side effects. But Mounjaro’s dual action may make these more frequent or intense for some users.
• Treatment Choice Is Personal: Medical history and personal tolerance play a role in deciding between weight loss medications. Your prescriber will review this and determine the best course of action, reducing the risk of serious side effects.

References

Semaglutide | Drugs | BNF content published by NICE. (n.d.). https://bnf.nice.org.uk/drugs/semaglutide.

Tirzepatide | Drugs | BNF content published by NICE. (n.d.). https://bnf.nice.org.uk/drugs/tirzepatide.

Aronne, L. J., Horn, D. B., Roux, C. W. L., Ho, W., Falcon, B. L., Valderas, E. G., Das, S., Lee, C. J., Glass, L. C., Senyucel, C., & Dunn, J. P. (2025). Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. New England Journal of Medicine. https://doi.org/10.1056/nejmoa2416394.

Website, N. (2025, August 6). Treatment. nhs.uk. https://www.nhs.uk/conditions/obesity/treatment/.

Jung, H. N., & Jung, C. H. (2022). The Upcoming Weekly Tides (Semaglutide vs. Tirzepatide) against Obesity: STEP or SURPASS? Journal of Obesity & Metabolic Syndrome, 31(1), 28–36. https://doi.org/10.7570/jomes22012.

Christophe, Hosn, O.A., Ghzayel, L. and Mourad, M. (2025). Exploring Connections Between Weight‐Loss Medications and Thyroid Cancer: A Look at the FDA Adverse Event Reporting System Database. Endocrinology Diabetes & Metabolism, [online] 8(2). doi:https://doi.org/10.1002/edm2.70038.

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