Wegovy vs. Mounjaro (semaglutide vs. tirzepatide)

Mounjaro (tirzepatide) and Wegovy (semaglutide) are weekly weight loss injections that can help you reach a healthier weight. They both work best alongside lifestyle changes, including a reduced-calorie diet and more physical activity. But there are also differences between them, meaning what suits one person may not be what’s best for you. Here, we’ll outline some of the key differences to help you make an informed choice.

Key takeaways

• Both Wegovy and Mounjaro are taken as a weekly injection at home.
• Wegovy targets one appetite hormone, while Mounjaro targets two.
• While Wegovy and Mounjaro work similarly to help you lose weight, they contain different ingredients and have different manufacturers.

What is Mounjaro?

Mounjaro is a prescription medication used to treat type 2 diabetes and support weight loss. It is manufactured by Eli Lilly and contains the active ingredient tirzepatide.

Mounjaro works by helping to regulate blood sugar levels, slowing how quickly food leaves the stomach, and reducing appetite. This can help people feel fuller for longer and eat less. It is taken as a once-weekly injection using a pre-filled pen and is usually prescribed alongside healthy lifestyle changes.

It is typically prescribed for people with a higher body mass index (BMI), or for those with a BMI of 27 or above who also have a weight-related health condition, such as high blood pressure or type 2 diabetes.

What doses does Mounjaro come in?

You can get Mounjaro in six strengths:

• 2.5 mg
• 5 mg
• 7.5 mg
• 10 mg
• 12.5 mg
• 15 mg

Your clinician will always give you the lowest dose (2.5 mg) to begin with, so you're less likely to experience side effects.

You’ll stay on each dose for at least four weeks to see how your body responds.

You don’t have to increase your dose. If you’re still dealing with any side effects well or you’re just comfortable with the weight you’re losing, you can stay on the same dose.

What dose do you start losing weight with?

No one’s weight loss journey on this treatment is exactly the same. How much weight you lose depends on how your body responds to Mounjaro.

The starter doses are mainly used to help your body adjust to the medication, although some people may notice early appetite suppression or initial weight loss. As the dose increases, the effects often become stronger, and many people start to see more noticeable weight loss from around 10 mg onwards.

What is the active ingredient in Mounjaro?

The active ingredient in Mounjaro is tirzepatide. It’s a type of drug called a dual agonist, which means it acts on two different appetite hormones to help control hunger and blood sugar levels.

What is Wegovy?

Wegovy contains the active ingredient semaglutide and is prescribed to help adults manage their weight long term.

It is usually recommended for people with a higher body mass index (BMI), or those with a BMI of 27 or above, who also have a weight-related health condition such as high blood pressure or type 2 diabetes.

Semaglutide is also used in the diabetes medication Ozempic, but Wegovy is licensed specifically for weight management.

What doses does Wegovy come in?

Wegovy comes in six different doses:

• 0.25 mg
• 0.5 mg
• 1 mg
• 1.7 mg
• 2.4 mg
• 7.2 mg

There’s also a 4.8 mg dose, but it’s only available off-label. It may be prescribed if the 2.4 mg dose is no longer providing the results you need, but the 7.2 mg dose is difficult to tolerate. Your myBMI clinician can review your progress and work with you to find the dose that best supports your weight loss journey.

Your clinician will use a six-step dosing schedule, as experts call it, to get you started on Wegovy. This means they’ll start Wegovy at a low dose and gradually increase it over 16-20 weeks to help your body get used to it.

But just like Mounjaro, you don’t have to move up a dose. You can stay on the dose that gives you the best results with the least side effects.

What dose do you start losing weight with?

You can start losing weight the moment you start treatment, but most weight loss happens gradually as the dose increases over time. There is no one-size-fits-all dose where weight loss begins, but as your dose increases, you should start to see better results.

If you’re taking Wegovy and feel unsure about your progress, your GP can review your treatment and make adjustments if needed.

What is the active ingredient in Wegovy?

The active ingredient in Wegovy is semaglutide. It belongs to a class of medicines known as GLP-1 receptor agonists, which help control appetite and blood sugar.

Administration

Both Wegovy and Mounjaro come in pre-filled injection pens that you use at home. The medication is injected just under the skin (a subcutaneous injection) once a week.

Both treatments are injected into the same areas of the body:

• Stomach (abdomen), at least a few centimetres away from the belly button
• Front of the thigh
• Upper arm

It is important to rotate injection sites each week. For example, you might use the left side of your stomach one week and the right side the next. This helps reduce irritation and prevents lumps forming under the skin.

While both medications are taken in a similar way, the pens themselves work slightly differently, so it is important to follow the instructions provided with your specific treatment.

Wegovy (injection)

Wegovy is taken once a week on the same day each week. You can take your injection at any time of day, with or without food.

Wegovy comes in a FlexTouch multi-dose pen. Each pen contains four doses, which means one pen typically lasts four weeks. You attach a new needle for each injection and use the dose selector to set the correct dose before injecting.

If you haven’t finished using your pen within 42 days of opening it, you need to return it to a pharmacy for safe disposal.

Where do you inject Wegovy?

You can inject Wegovy into your belly, upper arms, or thighs. If you use your belly, stay at least 5 cm away from your belly button. It’s also important to change where abouts you give the injection every week to avoid injection site reactions and irritation.

Mounjaro (injection)

Mounjaro comes in a KwikPen, with four doses per pen. This is also an injection you give yourself once a week that can be taken at any time of day, with or without food.

You need to dispose of your pen safely by returning it to a pharmacy if you haven’t finished it within 30 days of first opening.

Where do you inject Mounjaro?

Just like Wegovy, you can inject Mounjaro into your upper arms, thighs, and belly. But if you choose to inject your belly, remember to select a spot that’s at least 5 cm away from your belly button.

Mechanism of action

Both Mounjaro and Wegovy work by targeting hormones involved in appetite, blood sugar control, and digestion. These hormones help regulate how full you feel after eating and how the body manages glucose.

Both treatments are clinically proven to support weight loss when combined with lifestyle changes. Your clinician will consider factors such as your medical history, treatment goals, and preferences when deciding which option may be most appropriate.

GLP-1 receptor agonist (Wegovy)

The active ingredient in Wegovy is semaglutide, which is a GLP-1 receptor agonist. This means it mimics a natural hormone in the body called glucagon-like peptide-1 (GLP-1).

GLP-1 helps regulate appetite and blood sugar levels. It works by signalling to the brain that you feel full, slowing how quickly the stomach empties, and helping control blood sugar after eating.

By mimicking this hormone, Wegovy can help reduce appetite, support smaller portion sizes, and make it easier to maintain a calorie deficit, which supports gradual weight loss.

GLP & GIP receptor agonist (Mounjaro)

The active ingredient in Mounjaro is tirzepatide. It works by activating two hormones in the body: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide).

Like Wegovy, it mimics GLP-1 to help reduce appetite, slow stomach emptying, and signal fullness to the brain. It also activates GIP receptors, which play a role in blood sugar control and how the body stores and uses energy.

By activating both GLP-1 and GIP receptors, Mounjaro works on multiple pathways involved in appetite and metabolism. This dual action is why it is sometimes referred to as a dual incretin receptor agonist.

Effectiveness for weight loss

Both Wegovy and Mounjaro are effective weight loss treatments when used alongside diet changes and increased physical activity. Clinical studies show that people taking these medications typically lose more weight than those relying on lifestyle changes alone.

In clinical trials, weight loss is usually reported as the percentage of body weight lost, rather than a fixed number of kilograms or pounds. This allows researchers to compare results fairly across people with different starting weights.

Studies suggest that both medications can lead to significant weight loss, but some research has shown that Mounjaro may lead to slightly greater average weight loss in certain groups of patients. However, results vary between individuals.

How much weight you lose will depend on several factors, including your starting weight, how consistently you take the medication, your diet, and your activity levels and most importantly how your body responds to each dose. Regular weigh-ins and check-ins with your clinician can help track progress and make sure your treatment continues to work well for you.

How much weight can you lose with Wegovy?

In 72-week clinical trials, people taking the highest dose of Wegovy (7.2 mg) lost up to 21% of their starting weight.

For example, if you weighed 100 kg (220 lbs) at the start of a course of Wegovy, you could lose up to 21 kg (46 lbs), reaching around 79 kg (174 lbs) after six years.

How much weight can you lose with Mounjaro? 

In 72-week clinical trials, people taking Mounjaro at doses up to 15 mg  lost an average of 22.5% of their starting weight.

So a person weighing 100 kg (220 lbs) at the start of a course of Mounjaro might lose 22.5 kg (50 lbs) and weigh 77.5 kg (171 lbs) by the end of six years.

Which is more effective?

Both treatments show very similar weight loss results in clinical trials, but Mounjaro is generally considered slightly more effective.

Patients taking Mounjaro 15 mg lost an average of 22.5% of their body weight, while patients taking Wegovy 7.2 mg lost around 21%. This reflects the average results seen in clinical trials once patients had reached the highest doses of each medication.

Wegovy vs Mounjaro cost

Mounjaro is generally slightly more expensive than Wegovy. The exact cost can vary depending on the pharmacy and the dose prescribed.

In Ireland, both medications are usually available only with a private prescription and are not currently covered under the Drug Payment Scheme (DPS) when prescribed for weight management.

How much does Wegovy cost?

Wegovy usually costs between €170 and €355 per month. The exact cost can depend on which dose you’re taking and the pharmacy you go to.

How much does Mounjaro cost?

Mounjaro usually costs more. Prices range from €280 per month for 2.5mg to €580 per month for 15mg.

Comparing side effects

Both Wegovy and Mounjaro can cause mild, temporary side effects.  because they work on your digestive system. You’re most likely to notice side effects when you first start taking Wegovy or Mounjaro, or when you increase your dose, but they tend to resolve over time as your body adjusts to treatment.

Your doctor will increase your dose slowly, by small amounts, to ensure your body can handle the next dose.

If your symptoms don’t improve or get worse, be sure to talk to your prescriber.

What are the Mounjaro side effects?

If you’re taking Mounjaro, you might notice side effects like: 

• constipation  
• diarrhoea 
• indigestion 
• feeling sick or being sick
• low blood sugar, known as hypoglycaemia

How severe are the side effects of Mounjaro?

The side effects of Mounjaro are usually mild to moderate. They don’t tend to last long and often get better as your body gets used to the medication.

What are the side effects of Wegovy?

If you’re taking Wegovy, you might notice side effects such as:

• indigestion
• an upset or inflamed tummy
• feeing sick
• being sick
• acid reflux or heartburn

How severe are the side effects of Wegovy?

Like Mounjaro, Wegovy’s side effects are usually mild to moderate and don’t last too long.

Can I get help with side effects?

Your doctor can help with the side effects of taking Mounjaro or Wegovy. They may recommend:

• eating smaller, bland meals while you recover
• drinking plenty of water to stay hydrated.

 Your doctor may be able to offer you advice and treatment, where available, to manage any side effects that may be impacting your daily life.

Side effects overview

Side effects of Wegovy and Mounjaro involve the digestive system. They’re often mild or moderate and get better quickly. However, if you find them distressing, speak to your prescriber, who can adjust your dose and suggest remedies.

Seek urgent medical help if you experience:

• Severe pain in your tummy that doesn’t go away, which can be a sign of an inflamed pancreas
• Swelling around your face, tongue, or throat, which are signs of an allergic reaction
• Severe vomiting or dehydration, especially if you cannot keep liquids down

Availability

You can get both Wegovy and Mounjaro with a private prescription.

For both medications, a registered doctor will only prescribe if you have:

• a BMI of 30 or higher
• a BMI of 27 or over and a weight-related health problem like prediabetes, type 2 diabetes, or obstructive sleep apnoea

Is Mounjaro available to buy in Ireland?

Yes. You can buy Mounjaro to help you lose weight in Ireland with a private prescription.

How do I get a prescription?

A registered doctor can examine your health and confirm whether Mounjaro is right for you.

Is Wegovy available to buy in Ireland?

Yes. Wegovy is licensed in Ireland and available to buy in pharmacies with a prescription.

How do I get a prescription?

A registered GP or specialist weight management service can assess whether Wegovy or Mounjaro may be suitable for you. They will review your BMI, medical history, and any weight-related health conditions before deciding if you meet the criteria for treatment.

Comparing Wegovy and Mounjaro

Frequently asked questions

Is Mounjaro better than Wegovy for weight loss?

There is no ‘better’ treatment. Instead, it’s about finding the best treatment for you. Mounjaro has led to greater weight loss in some studies, but it also costs more, and Wegovy may be a better fit for your health and budget.

Talk to your doctor about the best option for you.

What is the downside of Wegovy?

The main downsides of Wegovy are digestive side effects and slightly lower average weight loss compared with Mounjaro in some studies. However, it can still support significant weight loss and is often slightly more affordable, which may make it a better option for some people.

What is 1mg Wegovy equivalent to in Mounjaro?

Most people reach 1 mg Wegovy after two dose increases. For people taking Mounjaro, the second dose increase will bring your dose to 7.5 mg. But they’re only “equivalent” in terms of the schedule. As they both contain different ingredients, there is no real dose-for-dose equivalent.

Your doctor will prescribe the dose that provides the best weight-loss without causing side effects.

Why do people switch from Wegovy to Mounjaro?

People may switch from Wegovy to Mounjaro if they are not responding well to treatment, weight loss has slowed, or side effects are difficult to manage.

How long does treatment last?

Wegovy and Mounjaro are designed for long-term weight management. Treatment usually continues for as long as it is helping you and remains suitable for your health.

Some people use the medication until they reach their goal weight, while others continue treatment longer term to help maintain their weight loss. Your clinician will review your progress regularly and help decide how long treatment should continue.

Summary of Wegovy vs Mounjaro

Wegovy and Mounjaro are both highly effective treatments that can help you lose weight. They’re used in the same way, as weekly injections, and they can cause similar, temporary side effects. While Mounjaro has shown a slightly greater long-term weight loss due to its dual-hormone action, Wegovy is still a very effective and slightly more affordable option for lots of people.

Speak with your prescriber about whether Wegovy or Mounjaro could help with your weight-loss journey.

Sources

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• Semaglutide vs Tirzepatide for Weight Loss in Adults With Overweight or Obesity. (2024). JAMA Internal Medicine. [Accessed on February 12, 2026]
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