The ultimate Mounjaro (tirzepatide) guide: weight loss, side effects, dosage & more

Medical weight loss is a topic of great discussion at the moment, with several weight loss medications on the market, including Wegovy, Ozempic, Saxenda, Orlistat, and Rybelsus.

However, the latest medication gaining traction is Mounjaro, and for good reason — this medication has proved to be incredibly effective for weight loss.

So, how does Mounjaro lead to weight loss outcomes? In this guide, we’ll explore what Mounjaro is, how it works, and how much weight you could potentially lose, especially when combined with healthy lifestyle changes.

What is Mounjaro?

Mounjaro (pronounced Mown-JARH-OH) is a dual-action medication that is highly effective for weight loss. This medication is delivered by subcutaneous injection once a week.

In official terms, Mounjaro is a long-acting dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist [1].

The active ingredient in Mounjaro is called tirzepatide. For context, medications like Wegovy, Rybelsus, and Ozempic contain the active ingredient semaglutide, while Saxenda contains liraglutide.

How does Mounjaro work?

Mounjaro works slightly differently from GLP-1 medications, like Wegovy, as it activates both GLP-1 and another hormone called GIP, which helps to promote fat loss, block fat gain, and regulate blood sugar.

By combining the effects of GIP and GLP-1, Mounjaro is more effective at promoting weight loss through decreased appetite, as well as directly impacting the pathways that lead to fat loss.

To simplify this a bit, this medication helps to reduce your appetite (making you feel fuller far more quickly), assists with turning down cravings, helps improve blood glucose levels, and stimulates the breakdown of fat.

Another difference between tirzepatide and a GLP-1 medication like semaglutide is the dosages. Mounjaro doses tend to be a bit higher than other weight loss injections, starting at 2.5mg and going up to 15mg. Wegovy, on the other hand, starts at 0.25mg and goes up to 2.4mg [2].

If you’re looking for a clearer picture of what progress might look like, check out this breakdown of expected weight loss results week by week using Mounjaro.

How effective is Mounjaro?

According to clinical trials, tirzepatide is one of the most effective medications for weight loss that is currently available. There have been a number of studies on the results of Mounjaro, and it outperforms other GLP-1 medications.

One study from July 2022 found an average of 19.5% body weight loss in patients on tirzepatide after 52 weeks, compared to average patients on semaglutide, who lost an average of 13.8% body weight over the same amount of weeks [3][4].

However, newer data on Wegovy, the more affordable and accessible GLP-1 weight loss medication, shows an average weight loss of 20.7% after 72 weeks [11] compared to 20.9% with Mounjaro at its highest dose [12], putting it nearly on par with Mounjaro in terms of effectiveness.

For more insight, we compared:

• Mounjaro vs Wegovy
• Mounjaro vs Ozempic

Can you switch from another GLP-1 medication to Mounjaro?

Switching from Wegovy to Mounjaro is possible, as generally you can move from another GLP-1 medication, like semaglutide or liraglutide, onto tirzepatide, but you'll need to consult with your healthcare provider on how best to do this.

It's important to note that regardless of the dose of your previous medication, you'll need to start on the lowest dosage of Mounjaro, which is 2.5mg, and slowly increase your dosage over time.

Can you switch from Mounjaro to Wegovy?

Yes! It is safe and straightforward to switch from Mounjaro to Wegovy. With Juniper, patients don’t need to restart at the lowest dose. If clinically appropriate, they can continue at a higher dose aligned with recent treatment history.

Plus, our switching protocol has only a 7-day gap between medications, compared to 28 days with most other providers. Our clinical oversight ensures safe, effective transitions — helping patients maintain momentum without compromising care.

You can switch in a few easy steps. Simply answer some quick questions about your medical history and goals and choose whether to continue on your current medication or switch to an equivalent dosage in the same trusted GLP-1 class of medications. From here, our clinicians will work with you to find the best treatment plan.

How to administer Mounjaro

As with other GLP-1 medications, tirzepatide is administered via a subcutaneous (under the skin) injection. While this can sound intimidating, it is something that people tend to get used to fairly quickly.

The Mounjaro KwikPen is a pre-filled pen that's designed for easy self-injection. Each pen contains 4 doses, which you'll inject once a week.

The best place to inject Mounjaro for weight loss is the upper thigh, upper arm, or stomach. Many medications of this nature are delivered like this because it allows for a slow, sustained rate of absorption, and your body can continuously deliver the medication at a low dose [5].

Plus, some medications simply aren't absorbed well by the digestive tract or are destroyed by the acid and digestive enzymes in the stomach, which is why an injection is preferred as it bypasses this process [6].

If you’re planning to travel or are unsure how to store your pen while on the move, here’s our guide to travelling with Mounjaro and proper storage tips for Saxenda, Ozempic, and other injectable medications.

What are the common side effects of Mounjaro?

As with all medications, there is a chance of experiencing side effects when using Mounjaro.

The most common side effects of Mounjaro are similar to those you may experience with other GLP-1 medications, like Wegovy, including nausea, vomiting, diarrhoea, abdominal pain, constipation, and indigestion. Some users also report more unusual side effects like sulphur burps, skin sensitivity, body aches, or feeling unusually tired.

Occasionally, users also report feeling colder than usual while on tirzepatide. This may be related to reduced calorie intake or metabolic changes.

The good news is that these side effects generally subside as your body adjusts to the medication and should calm down after a few weeks. If you're continuing to experience side effects, it's best to consult your healthcare provider or prescriber for advice.

How to manage the side effects of Mounjaro

For the short-term or milder symptoms associated with taking Mounjaro, it can help to try the following [7]:

• Eat bland, low-fat foods
• Eat smaller meals and stop when you're feeling full
• Increase both your water and fibre intake

If you're experiencing prolonged side effects, be sure to discuss these with your health practitioner, who may advise reducing the medication dose to help mitigate these symptoms.

Rare but serious side effects

There are a handful of more serious side effects that, while rare, can occur, so it's important to be across these. These include [8]:

• Hypersensitivity reactions: Serious hypersensitivity reactions, like anaphylaxis and angioedema, have been reported. Discontinue tirzepatide if a serious allergic reaction is suspected and seek medical advice.
• Gastrointestinal disease: The use of tirzepatide has been associated with gastrointestinal adverse reactions that could be severe.
• Acute gallbladder disease: This has occurred in clinical trials and shouldn't be used by people with a history of gallstones without cholecystectomy.

These concerns should be discussed with a healthcare provider when determining whether this treatment is suitable or not.

Can Mounjaro affect hair, hormones, or fertility?

Some people have questions about whether or not Mounjaro causes hair loss or affects reproductive health. While hair loss isn’t a known common side effect, some users do report it.

There’s also emerging research into Mounjaro’s effect on fertility, but it’s best to avoid treatment if you’re pregnant, trying to conceive, or breastfeeding.

Can lifestyle factors affect your experience on Mounjaro

Yes — factors like sleep, alcohol consumption, and even the timing of your dose can impact how you feel on Mounjaro. For example, some users notice insomnia or disrupted energy patterns, while others wonder if it’s okay to drink alcohol while on Mounjaro.

If you’re considering taking a dose early, here’s what to know about adjusting your injection schedule.

Who shouldn't take Mounjaro?

Tirzepatide can't be used by some of the population — below is a list of people who should avoid this medication [8].

• If you have a personal or family history of a type of thyroid cancer called medullary thyroid carcinoma (MTC)
• If you have Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
• If you are allergic to tirzepatide or any of the ingredients in Mounjaro
• If you are pregnant, breastfeeding, or actively trying to conceive
• If you have type 1 diabetes
• If you have a history of pancreatitis (note: people who have had a cholecystectomy may be able to commence treatment, but be sure to discuss this with your practitioner)
• If you take an insulin secretagogue or are on insulin therapy
• If you have non-proliferative diabetic retinopathy requiring acute therapy, proliferative diabetic retinopathy, or diabetic macular oedema

Some medications can interact with Mounjaro and reduce its effectiveness or increase side effects. Here’s a list of medicines you shouldn’t mix with tirzepatide — always speak to your prescriber before combining treatments.

Is Mounjaro available in the UK?

Yes, Mounjaro is available in the UK. It's a medication option we offer, alongside Wegovy, for those who are aged between 18 and 75 and meet our strict eligibility criteria.

The Juniper Programme takes a holstic approach to weight loss and includes treatment from UK-registered clinicians, health tracking and free, unlimited consultations with prescribers.

While Mounjaro is incredibly effective, it's GLP-1 counterpart Wegovy also encourages life-changing weight loss outcomes, and is often more affordable, making it favourable for long-term weight management.

At the end of the day, the best option depends on you, your body and your lifestyle. By taking the Juniper quiz, you can check your eligibility and kickstart, or restart, your journey towards a healthier and happier you. Juniper offers tailored treatment plans based on your needs, taking your experience with medication and goals into account.

Do you need a prescription to access Mounjaro?

The short answer is yes, Mounjaro is a prescription medication, so you'll need to check in with your doctor or healthcare professional before starting treatment. This helps ensure Mounjaro is the right medication for you, as well as informing you of any potential side effects.

Before prescribing Mounjaro, a doctor will review your medical history with you. By having a proper health assessment before starting Mounjaro, you can get the most out of your weight loss treatment.

How much does Mounjaro cost?

The cost of Mounjaro in the UK starts from £189 per month as part of the Juniper Programme. This includes more than just the medication — the programme is designed to help you lose fat while preserving muscle, with guided education via the Juniper app, and tools to build lasting habits around nutrition and movement.

To get the most value out of your treatment, it helps to follow a Mounjaro-friendly diet and maintain habits that preserve muscle mass, which can help avoid muscle loss as you lose weight.

Can you get Mounjaro on the NHS?

Yes, Mounjaro is available on the NHS for weight loss and can now be obtained at GP surgeries in England. Previously, only Wegovy and Saxeda were available on the NHS, however these could only be accessed with a referral to an NHS specialist weight management service.  

It’s important to note that while GPs can now prescribe Mounjaro, access is extremely limited and the eligibility criteria is incredibly strict. As such, officials are asking people to not approach their GPs about the weight loss medication unless they meet the following criteria:

Year 1

• BMI ≥ 40 (or ≥ 37.5 for some ethnic groups)
• 4 or more weight-related comorbidities (e.g. type 2 diabetes, high blood pressure, sleep apnoea)‍

‍Year 2

• BMI 35 to 39.9
• Still require 4 or more co-morbidities‍

‍‍Year 3

• BMI ≥ 40
• 3 or more co-morbidities

This staged approach will reach 220,000 patients across the first 3 years. A full rollout is planned over 8 further years, eventually covering patients with BMI ≥ 35 and at least one comorbidity.

What happens after stopping Mounjaro?

A common question is what happens when you stop using Mounjaro. While it’s possible to regain weight without ongoing support, there are steps you can take to maintain progress.

Learn more about weight regain after stopping Mounjaro, keeping the weight off, and how conditions like PCOS, ADHD, or HRT can affect your long-term plan.