Ozempic, Mounjaro or Wegovy: what’s the difference?

Losing weight isn’t easy, and for some people diet and exercise don’t shift the pounds on their own. If you’ve been looking into other options, chances are you’ve heard about weight-loss jabs. Ozempic, Mounjaro and Wegovy pop up in the news, on social media and all over our Talk boards, but it’s not always clear how they differ.

They’re often talked about as if they’re interchangeable, but they’re not. Each one has a different active ingredient, a different licence in the UK and slightly different effects.

We asked Dr Daniel Atkinson, Clinical Lead at Treated.com, and Jane Msumba, multi-award-winning pharmacist and founder of the Inner Glow Clinic, to explain the differences.

In this guide

Understanding Ozempic, Mounjaro and Wegovy

They might sound interchangeable, but they’re not. All three started life as diabetes drugs, with weight loss turning out to be a side effect that got plenty of attention.

Each has a different licence, dose and sometimes a different ingredient, so it’s worth knowing the differences before speaking to your doctor.

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What is Ozempic?

Made by Novo Nordisk, Ozempic contains semaglutide. It works by helping the pancreas release insulin where blood sugar is high, slowing digestion and reducing appetite. In the UK, Ozempic is only licensed for type 2 diabetes in the UK. Any use for weight loss is off-label

Because supply is limited and it’s primarily for diabetes, getting hold of it just for weight loss is difficult. Side effects usually crop up when you first start and are mainly digestive, but some users have also reported rapid weight loss that noticeably changes their appearance - sometimes called ‘Ozempic face’.

What is Mounjaro?

Mounjaro is made by Eli Lilly and contains tirzepatide. Unlike Ozempic, it acts on two pathways (GLP-1 and GIP), which improves blood sugar control and also helps reduce appetite.

As Dr Daniel explains: “Whereas GLP-1 medications target one hormone, tirzepatide mimics the effects of two hormones that can help manage blood sugar levels. GIP stimulates the release of insulin after meals, and GLP-1 is involved in regulating your appetite by telling you when you’ve eaten enough. Both hormones also influence other processes involved in blood sugar regulation.”

Mounjaro is approved in the UK for adults with type 2 diabetes, and separately for weight management if BMI is ≥30, or ≥27 with at least one weight-related condition. Side effects are similar to Ozempic and Wegovy - nausea, diarrhoea and reduced appetite are the most common - and doctors usually start patients on a low dose to make it easier to tolerate.

What is Wegovy?

Also from Novo Nordisk, Wegovy contains the same ingredient as Ozempic (semaglutide) but in a higher dose. It’s licensed specifically for weight loss in people who are obese or overweight with a weight-related health problem.

Because it’s a higher dose (up to 2.4 mg compared with Ozempic’s 2 mg), trials show it’s more effective for weight loss. Side effects are broadly the same as Ozempic, though some people find them stronger because of the higher dose.

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How these medications help with weight loss

All three mimic gut hormones that kick in after you eat, helping regulate appetite and blood sugar. The result: you feel fuller, eat less and avoid blood sugar spikes and crashes.

Ozempic and Wegovy act on one of these hormone pathways, while Mounjaro acts on two. Here’s how they differ.

How Ozempic works

Ozempic’s active ingredient, semaglutide, mimics the GLP-1 hormone your body makes after a meal. The weekly jab tells your brain and pancreas to:

slow digestion so you stay fuller for longer
signal that you’ve eaten enough, cutting cravings
release insulin when needed, helping keep blood sugar steady

It’s worth noting that Ozempic isn’t licensed for weight-loss treatment by the MHRA in the UK. As Dr Daniel confirms: “One misconception is that Ozempic is a weight-loss medication, when it’s only used off-label for this reason. It’s designed to help patients manage diabetes, but its effects on weight loss tends to be the focus of most news stories that cover it.”

How Mounjaro works

Mounjaro (tirzepatide) acts on two hormones instead of one. That seems to make it more effective in trials, as people lost more weight compared with semaglutide.

It switches on GLP-1 and GIP receptors to boost fullness
It improves insulin sensitivity and blood sugar control; its impact on fat storage is still being researched

Because it works in two ways, Mounjaro has shown stronger results in weight management studies.

How Wegovy works

Wegovy’s main ingredient is semaglutide too, just in a higher dose for weight loss. It works in the same way as Ozempic - reducing hunger, slowing digestion, lowering calorie intake - but packs a stronger punch, which can mean stronger side effects until your body adjusts.

How effective are these medications for weight loss?

The obvious question: do they actually work? Trials suggest yes - though how much weight people lose depends on the drug and the dose.

Ozempic vs Mounjaro

The SURPASS-2 trial compared Mounjaro (tirzepatide) with Ozempic (semaglutide) in people with type 2 diabetes. At higher doses, Mounjaro was more effective for both blood sugar control and weight loss.

Average weight loss in SURPASS-2 over 40 weeks:

Mounjaro 5mg: 7.7 kg (17 lb)
Mounjaro 10mg: 9.5 kg (21 lb)
Mounjaro 15mg: 11.4 kg (25 lb)

A 2025 study backs this up, in which US researchers found that tirzepatide generally led to more weight loss than semaglutide.

Can you use Ozempic and Mounjaro together for weight loss?

No. They both work on the same hormone pathways to control blood sugar, so taking them together won’t improve results and can increase side effects. It also raises the risk of low blood sugar. Doctors don’t recommend using them at the same time.

Ozempic vs Wegovy

Because both contain semaglutide, the real difference is dose. Wegovy goes up to 2.4 mg, compared with Ozempic’s maximum dose of 2 mg for diabetes.

In US trials of people with obesity (but not diabetes), Wegovy users lost an average of 14.9% of their body weight over 68 weeks alongside lifestyle changes. Ozempic does lead to weight loss too, but is typically less because of the lower dose.

Mounjaro vs Wegovy

There hasn’t been a direct trial comparing the two yet, though one’s in progress. Early studies suggest Mounjaro leads to more weight loss overall - up to around 22% of body weight compared with about 15% for Wegovy.

So, while Mounjaro looks the most effective in trials so far, individual response and side effects vary. Which drug works best for you will depend on your health, how your body reacts, and your doctor’s advice.

Keeping in touch with your GP during treatment is important

Mumsnet users on Ozempic, Mounjaro and Wegovy

“I started at bmi 32.4 13st 1lbs prediabetic for years and I'm now bmi 25.5 10st 4lbs 8.5 months later and it resolved all my high blood sugar and IBS symptoms, it’s literally changed my life. Do it now.” Histoscientist

“I'm still taking Ozempic. I've been on it for 18 months. I've lost over 4 stone but sadly I've plateaued for [the] last 3 months. So I stopped taking it for 2 months as was advised then started it up again to trick [my] body into losing more weight. In 3 months I've only managed to lose a further 2 lbs so disappointed. I still have a lot to lose. I might ask [my] GP if they can prescribe me Mounjaro when I go for [my] next check up/weigh in.” caringcarer

“I’m on Wegovy if that helps!! Not many of us though and some posters are very pro MJ.” Radioundermypillow

“I'm on Ozempic. Also prescribed due to diabetes. The first month was the starter dose but I did lose 8lbs, then I started the next level up last week and have lost a few more lbs. I felt car sick for a few days at first and then a lot of fatigue but it's all gone now. It would appear that in clinical trials Ozempic isn't as effective as some of the newer ones but it's doing wonders for my blood sugars (I have a CGM) and also joint pain is nearly gone so I'm cautiously optimistic.” Malariahilaria

“[...] I'm enjoying my life on MJ and don't ever want to come off but I think I'm going to have to because of the price increases.” MaryBerrysFannyHammock

Dosages and how they’re taken

All three drugs come as pre-filled injector pens for a once-weekly jab under the skin. You can do this yourself at home, usually in your stomach, thigh or the back of your upper arm. Rotating the injection site each week helps avoid irritation or lumps. You press a button, the jab goes in, then the used pen goes in a sharps bin.

Why doses increase gradually

With all three, you start on a low dose and build up slowly (a process called titration). This helps your body adjust and helps to limit side effects.

Typical dose schedules

Ozempic: Starts at 0.25 mg once a week for four weeks, then usually moves to 0.5 mg. Depending on blood sugar control, the dose may go up to 1 mg or a maximum of 2 mg.
Wegovy: Also starts at 0.25 mg, with the dose increased every four weeks until reaching the maintenance dose of 2.4 mg.
Mounjaro: Begins at 2.5 mg weekly. After four weeks this rises to 5 mg, and your doctor may then increase it by 2.5 mg every four weeks, up to 15 mg if needed.

Slowly increasing the dose makes the treatment more tolerable, improves blood sugar control and can help with steady weight loss. The right dose for you depends on how well you respond and what your doctor recommends.

Who can get these treatments?

Who’s eligible depends on your health and how each drug’s licensed in the UK. Your doctor will look at your medical history and decide if one is suitable.

Both Mounjaro and Wevogy are approved for weight management in the UK by the MHRA. They’re usually offered if your BMI is 30 or above, or 27 and above if you also have a weight-related condition such as high blood pressure, type 2 diabetes or high cholesterol.

Ozempic is officially licensed for adults with type 2 diabetes. Some doctors do prescribe it “off-label” for weight loss, but it’s not currently approved for that use in the UK, which means access through the NHS or insurance can be limited.

How do the costs of Ozempic, Mounjaro and Wegovy compare in the UK?

It depends on where you get them. On the NHS, Ozempic is only prescribed for diabetes, not weight loss.

Wegovy is generally cheaper than Mounjaro when bought privately, but prices vary between clinics. Private insurance rarely covers these drugs, so most people pay out of pocket if they’re using them for weight management.

And with Mounjaro prices going up from September 2025, it’s not yet clear what people will be paying privately.

Comparing common side effects

As with any medication, side effects are part of the picture. For Ozempic, Mounjaro and Wegovy, the most common concerns tend to involve the digestive system - nausea, diarrhoea, constipation or stomach pain. These usually appear when you first start treatment or increase the dose, and for most people they ease off as the body adjusts.

All medication has side effects [...] You look at the risks and make an informed decision along with medical consultations and advice 🤷‍♀️[The] same as literally any other drug.

BountifulPantry

Most side effects are mild and tend to ease once your body adjusts. Still, it helps to know what’s been reported with each drug.

Important: These medicines slow stomach emptying, which can affect how well some tablets (such as the contraceptive pill or certain painkillers) are absorbed. Extra contraception may be advised after a dose increase but seeking medical advice from your GP is sensible.

Ozempic side effects

Because Ozempic has been widely used for diabetes, its side effects are well studied.

Gastrointestinal issues are the main complaint: around 16 to 20% of people report nausea and about 9% diarrhoea. Vomiting, constipation, abdominal pain, fatigue and dizziness also occur, though less often.

Rare but more serious risks include pancreatitis, vision changes and allergic reactions. For people with diabetes on other medications, low blood sugar (hypoglycaemia) can also be a concern.

Dr Daniel adds: “In the US, people with a history of MTC or MEN2 are advised not to take these medicines. In the UK, these aren’t formal contraindications, but doctors may still avoid prescribing in such cases. Diabetic ketoacidosis is not treated with these drugs.”

Mounjaro side effects

Mounjaro’s side effect profile is similar to other GLP-1-based drugs, though because it works on two hormone pathways, some people notice the stomach issues more strongly. In studies, nausea was reported in 12 to 18% of users and diarrhoea in 12 to 17%.

Others noted reduced appetite, indigestion, abdominal pain, vomiting or constipation. Like Ozempic, it carries a small risk of more serious conditions such as gallbladder disease or pancreatitis. Any severe or persistent side effects should be flagged to a doctor quickly.

I've lost 67lbs, 50lbs of those on Mounjaro and honestly it's changed my life. Yes I've had a few slight side effects but it's nothing I couldn't handle.

ExplodingCarrots

Wegovy side effects

Wegovy contains the same ingredient as Ozempic but at a higher dose, so the side effects are largely the same but can be stronger. Nausea, diarrhoea, vomiting, constipation, stomach pain and fatigue are among the most common.

These are often worse during dose increases but usually improve once the maintenance dose is reached. Serious but rare side effects include pancreatitis, gallbladder problems and severe allergic reactions.

I started on Wegovy a month ago and it's been working for me. I did it because it has better trial results for other health benefits and I was happy to lose the weight slower and get all the other benefits [...]

YvonneLocker

Safety and long-term use

It’s natural to wonder about the long-term safety of these drugs, particularly if you’re thinking about using them for weight loss or alongside conditions like diabetes or heart disease.

Research is ongoing, but here’s what we know so far.

Ozempic: Has the most data behind it. Large trials show it not only helps manage blood sugar and weight but also lowers the risk of heart attack and stroke in people with type 2 diabetes and existing heart disease.
Wegovy: Since it’s the same ingredient as Ozempic, it’s expected to have similar heart benefits. Wegovy has also been approved by NICE for reducing cardiovascular risk in adults with obesity/overweight and established cardiovascular disease.
Mounjaro: Still relatively new, so long-term data is limited. Early results are promising, but it doesn’t yet have the same track record as semaglutide.

Which drug is best can depend on what matters most to you - whether that’s proven heart protection, stronger weight loss results, or tolerability.

Mounjaro, Ozempic, Wegovy - with all you need to use your time on them to massively change habits otherwise the research already shows people pack the weight back on.

curious79

Is one medication safer than the others for long-term use?

At the moment, semaglutide-based drugs - Ozempic and Wegovy - have the strongest safety record. Large trials show they not only help with weight loss and diabetes control but also reduce the risk of heart attacks and strokes in people with type 2 diabetes and heart disease.

Mounjaro is newer, so the long-term data isn’t as well established yet. Early results look positive, but if you’re particularly concerned about heart health, Ozempic or Wegovy currently have more evidence behind them.

Who should avoid these treatments?

These drugs aren’t suitable for everyone. All three carry a warning about thyroid C-cell tumours, which were seen in animal studies. It’s not clear if the same applies to people, but anyone with a personal or family history of medullary thyroid cancer (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2) should avoid them.

They’re also not recommended for people with a history of pancreatitis or known allergies to the active ingredients. And if you have a serious digestive condition such as gastroparesis (slow stomach emptying), these drugs can make it worse.

That’s why it’s important to go through your full medical history with your doctor before starting. It helps them judge whether the treatment is safe and suitable for you.

Join the conversation

Start a new discussion about your weight loss journey and get support from the Mumsnet community

Ozempic, Mounjaro and Wegovy all work in slightly different ways. The right drug for you depends on your health, what you want out of it, and how you handle the side effects. It’s something to weigh up with your doctor.

There isn’t a single “best” option for everyone. What works brilliantly for one person may not suit another. The safest way forward is to talk it through with your doctor, who can look at your medical history and help decide which, if any, is the right fit for you.

Useful links for more information

Always consult your healthcare provider for personalised medical advice regarding your weight management treatment options.

🔎 This article has been medically reviewed

Last reviewed in September 2025 by Dr David Porter MBBS, MSc, PgDip, an internationally renowned sports medicine physician and Founding Director of Opus.

Learn more

About the expert

Dr Daniel Atkinson is the Clinical Lead at Treated.com, an online healthcare service company.

About the author

Our resident Leeds lass, Rebecca Roberts is a Senior Content Editor here at Mumsnet. On a daily basis, she commissions, writes and edits content designed to help parents navigate real life - from product reviews to practical features on everything from sex and relationships to fashion and skincare.

Rebecca - aka Beccy - brings unique personal insight to weight-loss content here at Mumsnet, having undergone her own journey with medically supervised injections. Her firsthand experience with GLP-1 treatments provides authentic expertise that resonates with parents exploring similar options.

Beyond her role as an editor, she can be found balancing life as a working mum of two toddlers and when she’s not at her desk, you’ll likely find her at a PTA meeting, in a nearby coffee shop, or walking her two dogs up and down country lanes.