Mounjaro Injection Guide

Scientific research on medication is constantly evolving, bringing new, innovative ways to improve people’s health. One such way is Mounjaro, which is a weight loss drug and type 2 diabetes medication. It has seen rapid development over the last few years and is widely considered a safe and effective way to lose weight, making it a staple of weight loss treatments in the UK.

So, exactly what is Mounjaro, and what is it all about? This Mounjaro injection guide compiles a comprehensive list of frequently asked questions about the product and offers detailed support to help you determine whether Mounjaro is right for you.

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Mounjaro: What is it?

Mounjaro is a subcutaneous (under-the-skin) injection taken once weekly to regulate or reduce weight, treat type 2 diabetes, or both. Its versatility as a ‘dual agonist’ sets it apart from its contemporaries, as it targets two hormones in the body rather than one, thereby increasing its effectiveness. In trials, it has consistently shown total body weight reductions of up to 20%, thereby lowering the risk of weight-related health conditions.

Containing the active ingredient tirzepatide, Mounjaro is manufactured by Eli Lilly. It comes in the innovative “KwikPen” device, a multi-dose, pre-filled injection pen containing four doses of the treatment, enough for a full month’s worth of injections. The pen contains a mechanism that ensures you receive exactly the prescribed amount every time, saving you the hassle of having to worry about it yourself. Very fine needles can also be attached, which can be useful for individuals who are unsure about injecting themselves. All of this makes the Mounjaro KwikPen a convenient device that makes travelling more straightforward and reduces environmental waste compared to single-use injectors.

Mounjaro is injected at steadily increasing dosages, typically over a six-month period. This is done so your body can get accustomed to the medication in increments, thereby reducing the potential impact of side effects. After a few titrations (increases), you will reach the ‘maintenance’ dose, where you will typically remain for the remainder of your treatment.

Like all medications, Mounjaro can cause side effects, which are usually gastrointestinal in nature. These typically occur at the start of treatment or when you increase your dose, but will usually settle relatively quickly. Although highly effective for weight loss, tirzepatide may not be suitable for everyone, so you may find that an alternative is better for your unique circumstances.

What Does Mounjaro Do?

Mounjaro was initially approved only to treat type 2 diabetes, but was granted approval by the MHRA (Medicines and Healthcare products Regulatory Agency) for use as a weight loss treatment in late 2023. When paired with a healthy diet and regular exercise, it helps lower blood sugar levels, boost insulin levels, and regulate appetite.

Mounjaro is a long-term weight management treatment. It lowers your BMI (Body Mass Index) by slowing digestion, reducing appetite, and keeping you full longer.

How Does the Mounjaro Injection Work?

Mounjaro is a dual agonist, meaning the tirzepatide ingredient targets two hormones in the body simultaneously rather than one, to achieve greater results.

GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are the two hormones mimicked by Mounjaro and are responsible for reduced appetite and a prolonged feeling of fullness. Tirzepatide also boosts insulin secretion by the pancreas when blood sugar is high, reducing the risk of hypoglycemia. Mounjaro is the only dual agonist available in the UK, setting it apart from other options in its effectiveness.

As you progress through Mounjaro treatment, you will notice that smaller meals fill you up faster and hunger cravings diminish, leading you to consume fewer calories. By regulating glucose levels and controlling appetite simultaneously, Mounjaro can address the major issues in weight management at once: psychological, behavioural, and physical.

This provides an excellent foundation to then build upon with healthy eating and exercise.

Who Is Mounjaro For?

Mounjaro helps those who need support on their weight loss journey. To qualify for Mounjaro as a weight loss treatment, your BMI must be ≥ 30, or ≥ 27 if you have at least one weight-related health issue, such as type 2 diabetes, high blood pressure or sleep apnoea. Tirzepatide also functions as a treatment for type 2 diabetes, meaning it can be an important treatment for individuals who are dealing with both conditions.

Mounjaro

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• Approved Weight Loss Treatment
• Suitable for adults with a BMI of +30kg/m²
• Pre-filled injection pen

• Discreet delivery next working day
• Online prescription - No doctor visit

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Who Can’t Use Mounjaro?

For Mounjaro to be used safely and effectively, only the appropriate groups of people must take it. It should not be taken by pregnant individuals, those with digestive issues (including gastroparesis), pancreatitis, macular oedema, or diabetic retinopathy.

Other prescribed medicines may have an effect on the Mounjaro treatment or your overall health, as two drugs interacting within the body can cause harm. Antidiabetic drugs, other GLP-1s and some oral drugs are not recommended to be taken simultaneously. If you are breastfeeding, or planning to start, you should talk to your clinician before using Mounjaro.

If you are taking an oral contraceptive pill, Mounjaro will prevent it from being absorbed into the body, so a different form of contraceptive would be needed, such as a condom.

If you are unsure about any aspect of the treatment, speak to your clinician.

How Quickly Does Mounjaro Work?

In most cases, Mounjaro will begin to have positive effects on your blood sugar as soon as you start taking it, although visible weight loss changes will not happen overnight. Studies have shown that by the end of the first month, you may have lost an average of 4% total body weight. By the third month, this number climbs to 8%.

However, you should notice a drop in appetite within the first few days. Some people experience an immediate drop in weight, but this is just your body reacting to your new low-calorie diet and expelling glycogen-infused water as waste.

How Much Weight Do You Lose on Mounjaro?

There is no fixed amount of weight you are guaranteed to lose with Mounjaro, but multiple clinical trials have reported mean weight losses. One such trial found that, on average, Mounjaro reduces BMI by 25.3% by week 88, or roughly 20 months. The subjects were given either the 10mg or 15mg dosage.

It is important to remember that Mounjaro is not a miracle weight loss cure. It will make your diet and exercise changes more effective, but it still requires hard work and dedication. But this hard work can be very rewarding, as shown by before-and-after photos and customer reviews.

How Can I Maximise the Effects of Mounjaro?

To get the most out of Mounjaro, both diet and exercise are essential - this is called ‘wraparound care’. Starting with dietary adjustments, cutting down on calories and increasing your intake of lean proteins and fibre is advised. Fish, eggs, chicken and tofu are all great sources of protein, and pairing them with vegetables and bread will create a well-rounded diet.

It is best to avoid high-sugar foods, fried or processed foods, and alcohol as much as possible, but surprisingly, there are fruits and vegetables to avoid, too. Those with a high GI (Glycaemic index), despite being considered healthy in most cases, can cause a rapid spike in blood sugar. Oranges, pears, carrots and sweetcorn are all classed as having a high GI, so take this into your dietary considerations.

Cardiovascular exercise, such as cycling, walking, swimming or jogging, will all work well with the Mounjaro to increase calorie expenditure. About 2.5 hours per week of varied activity will greatly help reduce BMI.

Following your dosage schedule is another important way to support the Mounjaro treatment. A well-rounded night's sleep will also help, along with reduced stress levels. The more you help the Mounjaro do its job, the more it will help you.

Common Side Effects of Mounjaro 

Like all medications, Mounjaro has the potential to cause side effects, and you should be aware of them before committing to a treatment plan. The most common are gastrointestinal symptoms, which usually occur at the start of the treatment and when increasing the dosage:

• Nausea
• Diarrhoea
• Vomiting
• Constipation
• Abdominal pain

When dealing with these effects, your body will expel a lot of liquid, so staying hydrated throughout your treatment will be beneficial. Electrolyte-containing fluids will also help, along with eating more plain foods such as toast, rice, and crackers.

These Mounjaro side effects are typically mild to moderate in severity, but can lead to more serious health conditions. A further list of side effects can be found in the Patient Information Leaflet, including those that are less common. Always seek the advice of a clinician if your stomach problems are severe or persistent.

What are the Mounjaro Dosage Directions? 

In most cases, the first dose of Mounjaro will be prescribed at 2.5mg once weekly for 4 weeks. At this point, your dosage may be increased to 5mg, but this can vary. Your clinician will monitor your progress, and if the lower dose is well tolerated, they will increase it in 2.5 mg increments as needed, up to 15 mg.

It will take around six months to reach 15mg, but not everyone needs a dosage that high. Some will have reached their weight goal before that point, while others may be satisfied with their progress using a lower dose. See the visual guide to the dosage schedule below.

You must take only the prescribed dosage. This is for your own safety. If you miss a dosage and it has been four days or less, inject as soon as you remember, then continue on your next scheduled day. If it has been more than 4 days, do not take your missed dose; continue on your next scheduled day. You should never take a double dose to make up for a missed one. Mounjaro doses must be taken at least three days apart.

Microdosing is also not recommended. It has not yet been clinically trialled, and therefore, the effects are still unknown. Microdosing involves taking less than your prescribed dose to either save money or reduce side effects, but the health risks involved render it an unreliable method.

Remember, consistency is key. Try to take your Mounjaro at the same time and day each week. This will help your body adjust to the treatment, and a set-in-stone schedule should lessen the chances of forgetting that week's dosage.

Where Do I Inject Mounjaro?

Mounjaro needs to be injected into the fatty tissue under the skin. This could be your stomach, upper thighs or upper arms. If conducting the injection yourself, your stomach or thighs are recommended, as it would be difficult to reach your arm without the assistance of another person. Mounjaro has the same effect regardless of injection site, so the location comes down to personal preference.
 

It is advised to rotate your chosen injection site weekly. The same body part may be chosen, but alternating between the left and right sides will reduce the risk of infection. Guides on both how to inject and where to inject are available on our website.

Where Should I Keep the Mounjaro Pen?

The Mounjaro KwikPen initially should be stored in a refrigerator at 2 °C - 8 °C. After it has been used for the first time, it can be stored unrefrigerated for up to 30 days, provided it is kept below 30°C.

Never store the KwikPen in the freezer. If the pen has frozen, do not use it. Furthermore, if the pen is damaged, or the medicine is discoloured or cloudy, do not use it. The medicine should be colourless / slightly yellow. Use of a corrupted treatment can be harmful.

Do not discard the KwikPen with everyday household waste. Your clinician will advise you on how best to dispose of used pens.

Mounjaro: How Much Does it Cost?

At Prescription Doctor, Mounjaro treatments start from £169.99 per month for a 2.5mg dosage. This amount increases with the dosage, with the 15mg being priced at £298.99. Bundles are available to reduce the price when buying in bulk, lower monthly delivery fees, and ensure that you have enough pens to continue your dosage schedule uninterrupted. Ultimately, this is your treatment, and research into which payment plans will work best is essential. The table below outlines Mounjaro prices at Prescription Doctor: 
 

How Do Mounjaro Injections Compare to Wegovy Injections?

Mounjaro and Wegovy injections work very similarly. They are both administered once per week and mimic hormones to regulate BMI. The difference is that Mounjaro is a dual agonist, acting on two hormone receptors at once. Wegovy is a solo agonist, thereby making Mounjaro the more effective option in most cases.

When comparing the highest dosage after 72 weeks of a clinical trial, Mounjaro reduces total body weight by an average of 22.5%. By comparison, injectable Wegovy reduces it by an average of 14.9% over 68 weeks. Mounjaro is widely considered the better treatment for weight loss, but it may not be the best option for you personally.

One treatment may cause undesirable side effects, while the other doesn’t. One may have an ingredient that would cause an allergic reaction. Research is fundamental before starting either treatment, as it is not something to be rushed into.

There is also cost and availability to consider. The cost comparison at Prescription Doctor is as follows:
 

We offer a comprehensive breakdown of the differences in the two treatments, so you can easily find which one would work best for you.

Comparing Mounjaro Injections to Wegovy Pills

Wegovy is now available as an oral pill, which sets it apart from the Mounjaro injection. The ingredients and mechanism of action are the same as the Wegovy injection; it’s just the method of administration that is different As a result, Wegovy tablets remain a single-agent agonist, meaning their potential weight loss effects are less potent than those of Mounjaro.

When comparing clinical trials, the Wegovy pill averages slightly lower rates of weight reduction than the Wegovy injection, at 13.6%. This ranks it the lowest of the three compared methods, but despite this, it may be the most preferable option for some. Many dislike needles, and so a daily pill may suit them better than a weekly injection. It can also be easier to swallow a pill than to inject yourself or have another person inject you.

However, the pill needs to be taken on an empty stomach in the morning to take effect, whereas the injection can be administered at any time of day, regardless of when the food or drink was last consumed. Careful consideration and research of both options is important to determine which is best for you.

How Weight Loss Works with Prescription Doctor

No matter where you are in your weight loss journey, Prescription Doctor is here for you. We’ve been helping individuals reach their goals since 2013, and we’re ready to help you, too.

Apply for Mounjaro at your convenience by filling in our online questionnaire - no appointment, no phone call, no fuss. Our team of experienced clinicians will review your order to ensure the treatment is right for you before passing it on to our General Pharmaceutical Council-registered dispensing pharmacy, as an added layer of security. Finally, your medication will be delivered in plain packaging, right to your door, the very next day (if approved before 3pm on a weekday).

Our clinicians will be with you every step of the way, offering support and monitoring your progress to ensure everything runs smoothly. They are available to answer any questions or concerns you may have about your treatment - we only want what’s best for you.

We will support your weight loss journey from start to finish, but it can only begin with you. Start your consultation with Prescription Doctor today, and we’ll be happy to help with whatever you need.

Authored & Reviewed By

Mohamed Imran Lakhi

MPharm - Lead Pharmacist

Imran Lakhi is the superintendent pharmacist and founder at Prescription Doctor. He has been at the core of our team.

Published on: 11/01/2024 Re-Published on: 13/07/2026 Reviewed on: 13/07/2026