Mounjaro vs Wegovy: Which weight loss injection is right for you?

What's the difference?

You've heard about both Mounjaro and Wegovy. Both are injectable medications that help with weight loss. Both work on similar hormones in your body. But they're not the same drug, and which one suits you depends on your health, your goals, and how your body responds.

This guide compares them honestly so you can make an informed choice with your GP or pharmacist.

Quick comparison

Feature	Mounjaro	Wegovy
Active ingredient	Tirzepatide	Semaglutide
How it works	GLP-1 and GIP receptor agonist	GLP-1 receptor agonist
Injection frequency	Once weekly	Once weekly
Starting dose	2.5 mg	0.25 mg
Maximum dose	15 mg	2.4 mg
Approved for	Weight loss (and type 2 diabetes)	Weight loss only
Average weight loss	20-22% of body weight	15-18% of body weight
Cost	Typically £150-180 per injection	Typically £150-180 per injection

How Mounjaro works

Mounjaro contains tirzepatide. It activates two hormone receptors: GLP-1 and GIP. Both receptors help regulate appetite and blood sugar.

When you inject Mounjaro, it signals your brain that you're fuller than you actually are. You eat less naturally, without fighting constant hunger. It also slows how fast your stomach empties, so you feel satisfied longer after meals.

Mounjaro is licensed for weight loss and for type 2 diabetes. If you have diabetes alongside weight concerns, Mounjaro may offer a dual benefit.

How Wegovy works

Wegovy contains semaglutide. It activates the GLP-1 receptor only.

Like Mounjaro, it reduces appetite and makes you feel fuller sooner. It also slows stomach emptying. The main difference is that it works on one hormone pathway rather than two, which is why weight loss tends to be slightly less dramatic than with Mounjaro.

Wegovy is licensed for weight loss. It is not approved for diabetes.

Who Mounjaro suits

You might be a good fit for Mounjaro if:

You want the strongest average weight loss effect. Mounjaro users typically lose more weight than Wegovy users in clinical trials.

You have type 2 diabetes as well as weight concerns. One injection addresses both.

You've tried other weight loss medications and want to try a dual-action approach.

You tolerate GLP-1 medications well but want a stronger effect.

You prefer starting at a higher dose and titrating up more quickly.

Who Wegovy suits

You might prefer Wegovy if:

You want a well-established, single-action GLP-1 medication. Semaglutide has been used for diabetes for longer than tirzepatide.

You prefer a gentler starting dose and slower dose escalation. This can mean fewer side effects early on.

You have no diabetes diagnosis. Wegovy is simpler if weight loss is your only goal.

You've used GLP-1 medications before and know how your body responds.

You're concerned about cost and want the option with the longest track record of price stability.

Side effects and tolerability

Both medications cause similar side effects, most commonly nausea, vomiting, and constipation, especially when starting or increasing the dose.

Mounjaro side effects tend to be slightly more frequent because it's more potent. Some users report nausea lasting a few days after injection. Most side effects settle within the first few weeks as your body adjusts.

Wegovy side effects are generally milder because the starting dose is lower. The slower dose increase means your body has more time to adapt.

Both can cause dehydration. Drink plenty of water, especially if you feel sick.

Both can cause pancreatitis (very rare). Stop and seek urgent medical advice if you develop severe abdominal pain.

If you have a personal or family history of thyroid cancer, neither medication is suitable.

If you're pregnant, planning pregnancy, or breastfeeding, discuss with your GP before using either.

How to choose

Start with your GP or pharmacist. They know your full medical history and can rule out any contraindications.

Consider your weight loss goal. If you want the maximum effect and have tried other approaches, Mounjaro's stronger action may appeal. If you want steady, sustainable loss with fewer early side effects, Wegovy may suit you better.

Think about tolerability. If you've had nausea or side effects from other medications, Wegovy's gentler start might be easier. If you tolerate medications well, Mounjaro's faster escalation gets you to effective doses sooner.

If you have diabetes, Mounjaro offers the advantage of treating both conditions at once.

Cost is similar for both in the UK private market, so price shouldn't drive the choice.

The honest truth: both work. The "best" one is the one you'll stick with, tolerate well, and that fits your health picture.

Common questions

How long do I need to use these medications?

Both are designed for long-term use. You continue as long as they're working and you tolerate them. If you stop, weight often returns. Your pharmacist or GP will review your progress every few months.

Can I switch from Wegovy to Mounjaro?

Yes. If Wegovy isn't giving you the results you want, you can switch. Your pharmacist will advise on how to do this safely without doubling up on doses.

Do these medications work without diet and exercise?

They work better with them. The medication reduces hunger and helps you eat less, but moving your body and choosing nutritious food speeds results and improves overall health.

Will my weight come back if I stop?

Often, yes. These medications suppress appetite while you use them. Once you stop, appetite returns to normal. Some people maintain weight loss through habit change; others regain it. This is why they're designed for ongoing use.

Are these available on the NHS?

Currently, NHS availability is limited. Most people access them privately. Check with your GP surgery about local criteria.

How quickly will I see results?

Most people notice reduced appetite within days. Measurable weight loss usually appears within 2-4 weeks. Maximum effect takes 3-6 months as doses increase.

Can I use these if I'm on other medications?

Usually yes, but always tell your pharmacist or GP about everything you take. Some medications interact with GLP-1 drugs, particularly those for diabetes or blood pressure.

What happens if I miss an injection?

If you're a day or two late, take it as soon as you remember and resume your normal schedule. If it's more than a few days late, contact your pharmacist for advice.

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South Ealing Pharmacy in South Ealing, London offers online consultations for weight loss medication, with same-day assessment available. If you're considering Mounjaro or Wegovy and want personalised advice based on your health history, start your online consultation today. Our pharmacists will review your suitability, discuss side effects, and help you choose the right option for you.