Mounjaro questions answered: safety, side effects and how it works

What is Mounjaro?

Mounjaro is a prescription-only weight-loss treatment. It uses the active ingredient tirzepatide; a long-acting glucose-dependent insulinotropic polypeptide (GIP) receptor and GLP-1 (glucagon-like peptide-1) receptor agonist, to increase the body’s secretion of and sensitivity to insulin.

First approved for use in treating type-2 diabetes in 2022, Mounjaro is the brand name for tirzepatide; a long-acting GIP-analogue that activates the GLP-1 and GIP receptors, improving blood sugar control and slowing the movement of food through the stomach. 

While other well-known brands of weight loss medication such as Wegovy and Saxenda target just the GLP-1 receptors, Mounjaro is the first medication of its kind to combine this type of medication with the GIP agonist. 

This combination has been shown to boost the weight loss potential in users of Mounjaro, with tirzepatide showing an average weight loss of 17.8% compared to 12.4% for semaglutide users in clinical studies. 

The history of Mounjaro

While semaglutide has been around since the 1980s, Mounjaro is a much newer drug. First patented by Eli Lilly in late 2016, tirzepatide offered some improvement in the treatment of type-2 diabetes compared to semaglutide. However, the impact of tirzepatide on chronic weight management showed significant improvement compared to these older medication types.

Tirzepatide trails

As with any drug made available for human use, Mounjaro has been trialled and tested for safety and efficacy. In two randomised trials, tirzepatide was tested for weight reduction in 2,519 receiving the drug in once-weekly doses ranging from five to 15mg with a control group of 958 participants receiving a once-weekly placebo injection. 

After 72 weeks, all participants taking doses of tirzepatide experienced a significant reduction in weight compared to those receiving the placebo. The larger of the two trials saw those receiving the highest dose of Mounjaro lose 18% of their body weight on average. 

Is Mounjaro approved for weight loss?

Mounjaro was authorised for use by type-2 diabetes patients and overweight patients in the UK by the Medicines and Health Regulatory Agency (MHRA) in November 2023.

How does Mounjaro work for weight loss?

Mounjaro is a prescription weight loss medication that works by mimicking the actions of two naturally occurring hormones, GLP-1 and GIP. These hormones play key roles in regulating appetite, blood sugar levels, and digestion. By mimicking these hormones, Mounjaro leads to patients feeling full sooner after eating, and having less cravings for food. Additionally, it slows down the emptying of the stomach, making you feel fuller for longer and reducing your overall food intake.

Who can take Mounjaro?

Mounjaro is a prescription-only treatment. It can be used by eligible patients with a BMI of 30kg/m2 or more, or for those with a BMI of 27-30kg/m2, meaning respectively those who fall into the BMI categories of ‘obese’ and ‘overweight’. It is also used in patients with type-2 diabetes. You can work out your BMI using our calculator.

How to take Mounjaro

Mounjaro is administered in a pre-filled injection pen once a week. Patients using Mounjaro will start with a dose of 2.5mg, increasing to 5mg after four weeks. Further increases in dose might be recommended by a healthcare professional depending on the response to the treatment. 

The maximum dose of Mounjaro is 15mg once weekly. 

If you forget an injection of Mounjaro, you can take it up to four days, or 96 hours late. If you have missed this window, wait to take your next injection at the original scheduled time, and be cautious not to take two injections.

When administering a Mounjaro injection, you must not inject directly into muscle or veins, and make sure you avoid using the same injection point as in previous weeks. 

It is common to experience minor irritation at the injection site. This might present as redness and itching however these symptoms often go away quickly with proper aftercare. If you find that the irritation is escalating, causing you severe discomfort, or looks to be infected, you should speak to your health care professional.

Where to inject Mounjaro

Mounjaro should be injected under the skin of the stomach, thigh, or upper arm. If you choose to administer Mounjaro via the stomach or thigh you can administer by yourself, while administration via the upper arm will require help.

Exercise and diet

Mounjaro and similar weight loss treatments are designed to be used in conjunction with a healthy diet and exercise plan. Exercise and a healthy diet are an essential part of any weight loss journey and will help to enforce habits that ensure the results achieved through your course of Mounjaro are lasting.

What is the best diet for Mounjaro?

With all weight loss aides like Mounjaro, these drugs are designed to be used in conjunction with a healthy diet and regular exercise to achieve the best results. A balanced diet is a great way to optimise the effects of the drug. 

A healthcare provider will be able to offer dietary advice based on each case, however, generally a good place to start with diet changes is to cut down on high-fat foods and increase intake of fresh fruits and vegetables as well as protein and whole grains. 

Because Mounjaro makes users feel fuller for longer by slowing down the rate at which meals move through the stomach, eating balanced meals that are around half the size of meals users would previously eat will help to get the most from this process. Smaller meals help to avoid gastrointestinal side effects and can help to reduce the size of the user’s stomachs which increases the longevity of the drug’s effects.

Can I drink while using Mounjaro?

It isn’t known how Mounjaro interacts with alcohol use, however, your GP might advise you against drinking or to limit your consumption of alcohol. Alcohol has an impact on blood sugar levels, which Mounjaro aims to manage. As such, alcohol might limit the drug's capacity to work effectively. 

However, since a healthy diet is recommended in conjunction with the use of Mounjaro, limiting your alcohol consumption when using the weight medication can support your weight loss journey. Alcohol is high in calories, can encourage unhealthy eating habits and amplify cravings for greasy and high-fat foods. By reducing alcohol consumption while using Mounjaro, patients are more likely to get the best results from the drug.

What exercise should I do on Mounjaro?

Regular exercise remains a key element of any weight loss journey, even if medication such as Mounjaro is used. It is recommended to do between 30-60 minutes of exercise each day for a healthy lifestyle, however, those who are looking to lose weight should consider increasing their time spent exercising to achieve the best results. This might look like:

• Aerobic exercise such as walking, running, swimming and cycling

• Weight training to build resting metabolic rate

• Flexibility and balance training with yoga and stretches

Because Mounjaro is a prescription-only medication for those with a BMI indicating being overweight or obese, it might be easiest for users to start with low-impact exercise for shorter times and more often. For example, taking regular brisk walks might be a better way to get impactful exercise than trying to do long or fast runs straight away. 

Mounjaro side effects

Like all medications, Mounjaro has been seen to cause some side effects. It is not a guarantee that you will experience any side effects while using the drug, but it is wise to familiarise yourself with the common side effects users might experience. 

The most common side effects of Mounjaro are:

• Diarrhoea

• Feeling sick (nausea)

The most common side effects of Mounjaro are usually mild and will typically subside within a few weeks. These side effects are often the body's initial response to the introduction of an unfamiliar chemical and to mitigate these effects, Mounjaro is introduced gradually to give your body time to adjust to the treatment.

Common side effects of Mounjaro include:

• Fast pulse

• Mild to moderate allergic reaction, such as eczema, itching, or a rash

• Decrease in appetite

• Stomach pain

• Vomiting

• Constipation

• Indigestion

• Bloating

• Gas and burping

• Heartburn or reflux

• Fatigue

• An increase in the levels of pancreatic enzymes, which will show up on a blood test

• Itching, redness, or irritation at the injection site

Uncommon side effects of Mounjaro include:

• Gallstones

• An increase in calcitonin (a hormone that helps to control calcium levels)

In very rare cases, Mounjaro can cause a serious allergic reaction. This is known as anaphylaxis and causes breathing difficulties, throat, face and mouth swelling, and fainting.

Another rare side effect it can cause is an inflamed pancreas, known as acute pancreatitis. These side effects require urgent medical attention, so speak to your doctor or call 111 or 999 if you have intense and persistent stomach and back pain during treatment.

Always read the patient information leaflet for any treatment you are using or considering using.

How long does Mounjaro take to work?

Mounjaro will have an impact on blood sugar management in days and users will start to see the impacts on their weight in weeks. The most significant weight changes will be seen at higher doses of Mounjaro and with lifestyle changes such as regular exercise and a healthy diet. Always follow the recommendations of your doctors.

How much does Mounjaro cost?

Mounjaro is available through our Online Doctor service from £179. You will be required to carry out a consultation with our GP that starts by filling out some questions online. Our GP will then recommend the best treatment option for your needs and if appropriate, issue a prescription. 

Be aware that you might not get recommended Mounjaro based on your consultation.

How to get Mounjaro

Mounjaro is a prescription-only medication. You must meet set criteria to be prescribed Mounjaro by a registered healthcare professional. If you are interested in starting your weightloss journey and think you might meet the criteria for a tailored weight loss treatment, Pharmacy2U offer online consultations in which our GPs and pharmacists will assess your case and communicate with your NHS provider should you meet the requirements for a weight loss treatment such as Mounjaro.

Can you get Mounjaro on the NHS?

As of 2024, Mounjaro can be prescribed through the NHS for those living with type-2 diabetes or obesity. As an independent pharmacist, you could get access to a Mounjaro prescription via Pharmacy2U if one of our qualified GPs recommends the medication following a consultation - and we strive to deliver a quick service that gets you access to healthcare advice when you need it.

Mounjaro vs Ozempic

Mounjaro and Ozempic are both injectable medications that contain glucagon-like peptide 1 (GLP-1) receptor agonist. They are both used to manage blood sugar levels, but while Mounjaro is permitted for use under prescription in the UK for weight loss purposes, Ozempic can only be prescribed for the treatment of type-2 diabetes. 

If you are overweight and recommended a weight loss treatment to support your weight loss journey, you will not be offered Ozempic.

Start your online consultation with Pharmacy2U

If you are looking to kickstart your weight loss journey, you might be able to utilise a weight loss medicine to help you achieve your desired weight. The first step to finding out if Mounjaro is the right treatment for you is to fill out our online consultation form. One of our qualified GPs will take a look at your answers and recommend a suitable course of action, which might include a private prescription for Mounjaro or another type of weight loss treatment. 

As you may have heard, our supplier, Lilly, has announced that from 1st September, the price of Mounjaro in the UK will be increased for all providers. Because of this, we are currently prioritising existing patients. However, if you are considering weight management, there are alternative options available. 

You can get started with your weight loss consultation via our online consultation form.

Advice and information to support weight loss