Mounjaro vs Wegovy: key differences and which one works the best?

Choosing between Mounjaro and Wegovy can feel confusing, especially when both can support weight loss and share similarities. This guide explains how they differ, what to know about results and side effects, and how to find out which treatment may suit you best.

Article summary

• Wegovy and Mounjaro are prescription weight loss treatments. Wegovy is available as a weekly injection or morning tablet, and Mounjaro is as a weekly injection only.
• Both treatments can cause side effects, most commonly including nausea, vomiting, diarrhoea, constipation and stomach pain but they may settle as you get used to the medication.
• There’s no single “best” option. The right treatment for you depends on your health, your goals, and how you’d like to take it.

What's the difference between Wegovy and Mounjaro?

Both Wegovy and Mounjaro are once-weekly injectable weight loss treatments, but they include two different active ingredients.The active ingredient in Wegovy is semaglutide, which mimics a gut hormone called GLP-1. GLP-1 helps you feel fuller, and slows how quickly your stomach empties which could help you to think less about food. [1]

The active ingredient in Mounjaro is tirzepatide, which mimics GLP-1 and a second hormone called GIP. This dual action is thought to be part of why, in clinical trials, Mounjaro produced slightly greater average weight loss than Wegovy. [2]

Wegovy is also available as a once-daily tablet, which gives you a needle-free option if injections aren't for you. [3]

Wegovy vs Mounjaro Difference Table

*At the highest dose, alongside a healthy, calorie-controlled diet and increased physical activity. Figures for the Wegovy Pill come from a separate trial with different people and designs, so they aren't a head-to-head comparison. Individual results vary. Prices from MedExpress may change.

Weight Loss Results

Mounjaro and Wegovy are both proven to be effective at aiding weight loss in clinical trials.

• Mounjaro (SURMOUNT-1): adults taking tirzepatide 15mg lost an average of 22.5% of their body weight over 72 weeks. [2]
• Wegovy Pen (STEP UP): adults taking semaglutide 7.2mg lost an average of 20.7% over 72 weeks. [1]
• Wegovy Pill (OASIS 4): adults taking oral semaglutide 25mg lost an average of 16.6% over 64 weeks. [3]

It’s important to note that the best results come from combining weight loss treatments with lifestyle changes like a reduced-calorie diet and increased physical activity.

Wegovy vs Mounjaro Side Effects

Everyone responds to new medications differently, so you may experience different mild side effects from Mounjaro and Wegovy. [4] Generally, the most common side effects some patients report include:

• Nausea
• Vomiting
• Constipation
• Diarrhoea
• Headaches
• Fatigue
• Stomach pain
• Redness or itching around injection site (doesn’t apply to Wegovy Pill)

Rarely, these injections can cause more serious adverse side effects, including acute pancreatitis (inflamed pancreas), and anaphylaxis (serious allergic reaction). [4]

The main symptom of acute pancreatitis is severe, persistent stomach pain that may spread to your back. You may also have a high temperature and feel sick or be sick (nausea and vomiting).

If you have symptoms of pancreatitis, seek urgent medical attention straight away by calling 999 or going to A&E.

Anaphylaxis is a rare but life-threatening allergic reaction that happens very quickly. Signs can include:

• Difficulty breathing, fast breathing or wheezing
• Tightness in the throat, or trouble swallowing
• Feeling faint, dizzy or confused, or collapsing
• Swelling of the lips, mouth, tongue, or throat

If you notice any of these symptoms in yourself or someone else, call 999 or head to A&E right away.

Safety

Both Wegovy and Mounjaro are licensed in the UK for weight management and have been studied in clinical trials. [1-3] Like all medicines, they aren't suitable for everyone.

You shouldn't take either treatment if you're pregnant, planning a pregnancy or breastfeeding. They may also not be suitable if you have a history of pancreatitis, certain gallbladder problems, or are taking some other medicines. [5]

It is also important to note that Mounjaro can make the oral contraceptive pill less effective, so you must use an additional non-oral or barrier method (such as condoms) for the first 4 weeks of using Mounjaro, and 4 weeks after each dose increase. On the other hand, Wegovy doesn't reduce the effectiveness of the contraceptive pill. [5]

If you experience vomiting within 3 hours of taking an oral contraceptive, or diarrhoea that has lasted for over 24 hours, you may need to take the pill again to avoid unwanted pregnancy. You should call 111 for advice about this. [5]

Wegovy vs Mounjaro Cost

At MedExpress, the Wegovy Pill is the lowest-cost option to start, followed by the Wegovy Pen and then Mounjaro.

Prices usually rise as you move up to higher doses. If budget is part of your decision, it's worth thinking about the cost of the dose you're likely to stay on, not just your first month. You can see every dose and its price on each treatment page. Please note that treatment prices are subject to change.

Dosage

Both treatments start at a low dose and may increase gradually every 4 weeks. This gives your body time to adjust and helps keep side effects to a minimum. However, this is the minimum amount of time that you should allow between each dose increase. Everyone is different and you should follow a titration schedule that suits your response to treatment.

• Mounjaro: starts at 2.5mg once a week. The dose can go up in 2.5mg steps, to a maximum of 15mg. [2]
• Wegovy Pen: starts at 0.25mg once a week, increasing through 0.5mg, 1mg, 1.7mg, 2.4mg and finally 7.2mg. [1]
• Wegovy Pill: starts at 1.5mg once a day, increasing through 4mg and 9mg to 25mg. Take it first thing in the morning on an empty stomach (after an 8 hour fast) with a small sip of plain water (up to 120ml), then wait 30 minutes before eating, drinking or taking other medicines. [3]

You won't necessarily need to reach the highest dose. If you’re happy with your weight loss progress and how you’re tolerating side effects, you can remain on a lower dose for longer.

Wegovy vs Mounjaro FAQs

How do I choose what's better for me?

There's no one-size-fits-all answer, and that's okay. The "best" treatment is the one that suits your health, your goals and your day-to-day life. A few questions can help:

• How would you prefer to take it? If you'd rather avoid needles, the Wegovy Pill is a daily tablet. If you'd prefer to think about your treatment once a week, the Wegovy Pen or Mounjaro may suit you better.
• Does a morning routine work for you? The Wegovy Pill needs to be taken in a strict and specific way: on an empty stomach with a 30-minute wait before any other food, drink or medications. The injections have no such restrictions.
• What matters most in terms of results? Mounjaro showed the highest average weight loss in its clinical trial, [2] but all 3 led to significant weight loss results.[1,3]
• What fits your budget? Think about the ongoing cost of the dose you're likely to stay on.
• Do you take the contraceptive pill? Mounjaro reduces its effectiveness, so additional non-oral or barrier methods of contraception are necessary.

Can I switch from Wegovy to Mounjaro, or Mounjaro to Wegovy?

Yes, many people switch between treatments. This could be because of side effects, results, cost or a change in what suits their routine. Any switching would be reviewed by a prescriber.

Wegovy and Mounjaro contain different medicines, so there's no exact dose-for-dose match. Your prescriber will review which dose you should start the new treatment on, based on your current dose, how long you've been taking it and how well you've tolerated it. You'll usually take your first dose of the new medicine when your next dose of the old one would have been due.

You can also switch between injectable medication and oral medication. Again, your prescriber will review the right starting dose based on your individual circumstances.

Starting a weight loss treatment may feel daunting, especially since multiple branded treatments are now easily accessible. Likewise, if you've been using Mounjaro, you may now be looking for a more cost-effective alternative treatment like Wegovy.

It’s important to know the difference between treatments before deciding which one is right for you. Mounjaro and Wegovy are two of the most popular weight loss medications currently on the market. We explore the difference between the two to help you understand which is right for your weight loss goals.

“Choosing between Wegovy and Mounjaro isn’t simply about comparing weight loss percentages or body shapes in the mirror. Both treatments can support meaningful results, but the right option depends on your health, goals, preferences and how well you tolerate the medication. A consultation from a qualified pharmacist can help you make a safe, informed choice and feel supported throughout your treatment.” Dr. Sophie Dix, (BSc, PhD)

Head of Medical Affairs

At MedExpress, we offer online consultations with regular clinical check-ins, and a range of weight loss treatments including Mounjaro, Wegovy Pen, Wegovy Pill and Foundayo and our team can help you find the right treatment for you.

References:

1. Collins L, Costello RA. Glucagon-like Peptide-1 Receptor Agonists [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551568/
2. Latif W, Lambrinos KJ, Rodriguez R. Compare And Contrast the Glucagon-like Peptide-1 Receptor Agonists (GLP1RAs) [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572151
3. Wharton S, Lingvay I, Bogdanski P, Duque do Vale R, Jacob S, Karlsson T, Shaji C, Rubino D, Garvey WT; OASIS 4 Study Group. Oral Semaglutide at a Dose of 25 mg in Adults with Overweight or Obesity. N Engl J Med. 2025 Sep 18. Available from: https://pubmed.ncbi.nlm.nih.gov/40934115/
4. Inclusive Health Primary Care Network (PCN). GLP-1 Injectable Treatments Patient Information Leaflet [Internet]. Inclusive Health PCN; [cited 2026 Oct 12]. Available from: https://practice365.co.uk/uploads/sites/894/2025/10/GLP1-Intiation-Patient-Information-Leaflet-12-09-25.pdf
5. Faculty of Sexual and Reproductive Healthcare (FSRH). FSRH recommendations on GLP-1 agonists and oral contraception [Internet]. London, UK: Faculty of Sexual and Reproductive Healthcare (FSRH); 2025 Jan [cited 2026 Oct 9]. Available from: https://www.cosrh.org/Common/Uploaded%20files/documents/CEU-statement-GLP-1-agonists-and-contraception.pdf?UNLID=2221402612025222105455
6. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine [Internet]. 2022 Jun 4;387(3). Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2206038