Mounjaro Weight Loss Injection

What is Mounjaro?

Mounjaro is an injection which can help with weight loss, and it is prescribed to people with a certain BMI or those who have elevated high blood sugar levels due to type 2 diabetes. Its active ingredient is tirzepatide and the brand name is Mounjaro.

The drug comes in an injection pen, which can be given once a week in order to promote a feeling of fullness and reduce food cravings. Whether you take it for diabetes or weight loss, Mounjaro has to be taken in conjunction with an exercise and diet plan and it is only available on private prescription. In the UK, it was first approved for weight loss in November 2023.

How does Mounjaro work?

Mounjaro is the first medication to imitate two hormones which can help reduce appetite, food cravings and blood sugar. The active ingredient, tirzepatide, acts as a receptor to these hormones, which are:

Glucagon-like peptide-1 (GLP-1)
Glucose-dependent insulinotropic polypeptide (GIP)

Mounjaro helps with weight loss, as it increases the amount of time your stomach takes to empty, meaning you feel fuller longer than you normally would. You also feel fuller, even though you are eating less, as it works on brain parts which control hunger and appetite.

The two hormones above also increase the body’s production of insulin, the hormone responsible for maintaining and reducing blood sugar levels. Mounjaro helps to control high levels of blood sugar for patients with type 2 diabetes, but it can also aid weight loss by reducing blood sugar spikes, as food cravings can be caused by unregulated blood sugar. Because it can affect both your appetite and blood sugar levels, it can help reduce calorie intake without craving snacks in between regular meals, making it effective for weight loss.

How long does it take for Mounjaro to work?

While it should begin to work immediately, you may have to wait a few weeks to experience the full effect of Mounjaro, due to the fact that the dosage is increased gradually to reduce the risk of side effects.

For some of those given the largest dose, 15mg, in order to lose weight, it was found that many lost up to 22.5% body weight. But to get the best overall effect, it’s important to take Mounjaro alongside lifestyle changes such as a well-balanced diet, no snacking between meals and carrying out 150 minutes exercise a week.

How to take Mounjaro

For weight loss, your dose of Mounjaro should be injected once a week and on the same day of the week at the same time, as this helps keep the tirzepatide levels steady in the bloodstream. This means its effectiveness is increased and the risk of side effects is reduced.

At Amiry & Gilbride, we stock the multi-dose pen version of Mounjaro. Each pen contains 4 of the same strength dose. It’s important to carefully read and follow the patient information leaflet inside the box and your GP’s instructions.
Mounjaro should only be injected into the upper thighs or belly and you should avoid muscles or veins. It is possible to inject the dose into the upper arms, but only if you have a substantial outer layer of skin and someone can help you.
A new needle should be used every time and you should dispose of it safely into a sharps bin.
Check the pen and needle for any signs of damage before use and don’t use it if it’s bent or is unsealed. Also look at the liquid to check it is not cloudy or has become discoloured. If it is not completely clear and has become slightly yellow, it’s best to use a new pen.
Always check your Mounjaro dosing schedule before you administer it and that it’s the right medication and the right dose. This is particularly important for patients who take other injected medications such as insulin.

Where should I inject Mounjaro?

Ideally, Mounjaro should be injected into the upper legs or the stomach. When injecting into the stomach, leave a gap of at least 5cm away from your belly button. Although you aren’t likely to suffer irritation or soreness by the injection site as the dose is only injected weekly, choose a different place each time. This can mean the same area, just a different patch of skin.

Should I take Mounjaro with food?

Because Mounjaro is not taken by mouth, you can take it with or without food, depending on what suits you and your daily routine best.

When is the best time to take Mounjaro?

While it’s important to take Mounjaro on the same day and at the same time each week, it doesn’t matter when you take it. Once you’ve found the best time for you, it’s useful to set a reminder or alarm to alert you when the next dose is due. If necessary, you can change the time and day of injection, but this should only happen occasionally.

Is Mounjaro used long term?

Yes, Mounjaro can be safely used as a long-term treatment for weight loss and also type 2 diabetes. If taking it to aid weight loss, it’s normal to stop it once you have reached your ideal weight. If you are not losing the amount of weight expected or you have strong side effects, your doctor may tell you to stop taking Mounjaro.

Mounjaro dosage

The medication will come with a dosing schedule which allows for a slow increase of the dose. This is done to minimise common side effects, which include nausea and vomiting. It doesn’t matter which dose you are prescribed, you will still only have 1 dose per week.

You’ll start with a 2.5mg dose of Mounjaro per week for a total of 4 weeks, before increasing it to 5mg for the next 4 weeks. The dose can then be increased every 4 weeks, up to a maximum of 15mg. Your doctor will look at how the dose is working on you and check for any side effects before telling you to increase your dose.

We have the following doses available, and the dose relates to the amount of Tirzepatide in each injection:

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

This is how much tirzepatide is contained in each injection.

What is the starting dose of Mounjaro?

2.5mg for 4 weeks is always the starting dose for every patient. This is still the case even if someone is swapping from another weight loss treatment or has previously used Mounjaro.

What is the recommended dose?

The biggest weight loss is experienced once the maximum dose of 15mg has been reached, but it depends on how your body responds to the drug and whether you experience any side effects.

NB: Never take a dose higher than recommended by a doctor, as this increases the risk of severe illness and strong side effects. It could mean you have to pause or even stop your treatment, which will hamper your weight loss.

What if I miss a dose?

If a dose of Mounjaro is missed, there are a couple of rules depending on how much time has passed since the last dose was due.

If 4 days or less have passed since the last dose was due, you should take it as soon as you realise. Once this is done, you can continue your treatment as normal at the usual time and day, even if you end up having 2 doses less than a week apart.
If more than 4 days have passed, you should skip the dose which has been missed and continue treatment from when the next dose is due.

Which factors can affect my dosage?

Key things which can affect your dosage include:

How long you have been taking Mounjaro
Whether you’ve experienced side effects
How much weight has been lost on the current dosage
The number of any doses missed, as you may have to remain on a lower dose

Most people follow the dosing schedule, which means they start on a lower dose and increase it every 4 weeks.

How effective is Mounjaro?

Before Mounjaro was approved as a weight loss medication in the UK, there were Several studies done into its effectiveness.

85% of people injecting tirzapetide once every week were found to have lost at least 5% of their body weight after 72 weeks in The SURMOUNT-1 clinical trial. The higher the dose injected, the more weight was lost, as shown in the table below:

Average weight loss (the percentage of weight lost compared to starting body weight)	Weekly dosage of tirzepatide (Mounjaro)
16%	5mg
21.4%	10mg
22.5%	15mg
2.4%	Placebo

Mounjaro vs Wegovy

Both of these weight loss medications have been deemed effective. Which works best will depend on how your body responds. It may be that your doctor decides only one is suitable or there may be another one that works best for you. Both work in similar ways, although Mounjaro is what is known as a dual agonist, because it acts against two hormones, unlike Wegovy.

	Mounjaro	Wegovy
Active ingredient	Tirzepatide (GLP-1 and GIP receptor agonist)	Semaglutide (GLP-1 agonist)
Recommended dose	2.5mg to 15mg	0.25mg to 2.4mg
Most common side effects	nausea, vomiting, diarrhoea, constipation, abdominal pain/discomfort	nausea, vomiting, constipation, abdominal pain/discomfort, fatigue, headache
Frequency	Weekly	Weekly
Approved for	Weight loss and type 2 diabetes	Weight loss
Does it require a prescription?	Yes	Yes
% of people who lost 5% or more of their initial body weight	96.3% by week 72, on a dose of 15 mg a week	83.5% by week 68, on the highest dose of 2.4 mg a week

As can be seen in the above chart, clinical trials have shown that Mounjaro and Wegovy have similar results. Each medication has not been tested in the same study or for the same amount of time, so they are difficult to compare and it’s impossible to say which one is more effective.

Is Mounjaro available without prescription?

No, you cannot get Mounjaro without a prescription, because tirzapetide is a drug which is prescription only.

Will Mounjaro be available on the NHS?

In the UK, Mounjaro is still being reviewed by the National Institute for Health and Care Excellence (NICE). This means that although it is approved for weight loss, until the NICE assessment is concluded, the NHS won’t release its recommendations for who might be eligible for it on prescription.

Mounjaro side effects

Not everyone will suffer from side effects, but these are very common, whether it’s being taken for diabetes or weight loss:

Nausea
Vomiting
Diarrhoea
Constipation
Low blood sugar, if it’s being taken with some diabetes medications

These side effects are most likely to occur when you first begin taking Mounjaro, although they are not usually severe. The medication is gradually introduced to minimise these side effects while your body adjusts to it. If you do experience any of these common side effects, they should get better within just a few weeks. If they persist, you should speak to your doctor.

When taken with other type 2 diabetes medication such as insulin, Mounjaro can cause low blood sugar. The symptoms of this include dizziness, shaking, sweating, hunger and increased heart rate.

Common side effects of Mounjaro include:

Constipation
Stomach pain
Indigestion
Bloating
Heartburn or reflux
Gas and burping
Fast pulse
Mild/moderate allergic reaction such as itching, rash or eczema
Low blood pressure
Dizziness
Fatigue
Hair loss
Increased levels of pancreatic enzymes – these will show on a blood test
Irritation, redness or itching at the site of injection

Uncommon side effects include:

An increase in calcitonin – a hormone which helps keep calcium levels under control
Injection site pain
Weight loss
Gallstones
Low blood sugar (when used alongside metformin)
Acute pancreatitis (an inflamed pancreas) – if you experience severe back or stomach pain which doesn’t go away you should speak to your doctor immediately

Mounjaro may cause other side effects: please read the patient information leaflet for a full list.

Are there any long-term side effects?

There are no long-term side effects known to be caused by Mounjaro. If you do experience any, they should get better or go away completely within a few weeks or when you stop taking Mounjaro.

How to manage the side effects of Mounjaro

To try and avoid any side effects, you can:

Stay hydrated
Take Mounjaro at the same time on the same day every week
Only take the prescribed dose and do not increase it unless instructed to do so by your doctor
Eat plenty of fibre
If needed, take anti-diarrhoea tablets
Inform your doctor if your side effects are troubling you and not going away
Talk to your doctor about any other medications you take which may react with Mounjaro to cause side effects
Manage nausea by avoiding heavy, greasy meals, eating smaller amounts more often and sipping cold water

Who can take Mounjaro?

Mounjaro can be taken for weight loss for those who have:

A BMI of 30kg/m2 or more – obese
A BMI of 27kg/m2 or more – overweight and a weight-related problem or risk factor like high blood pressure

If you are allergic to tirzepatide or any other ingredients in Mounjaro, you should not use it. It should only be taken by over 18s and it is not recommended for those who are pregnant or breastfeeding.

Before using Mounjaro, you should speak to your doctor if you have any of the following:

An eye condition such as diabetic retinopathy
If you’ve ever had pancreatitis
A severe health condition such as gastroparesis, which affects your stomach emptying

Interactions with other medications

Mounjaro may react with other drugs, so it’s important to speak to your doctor if you take any over-the-counter, prescription or herbal medications. You should also talk to your doctor if you use any other diabetic medications, especially sulphonylurea or insulin.

Interactions with food/drinks

Although no food or drink reacts with Mounjaro, you may wish to avoid consuming excess alcohol, as this can affect levels of blood sugar and weight, making Mounjaro less effective.

Is Mounjaro the same as Wegovy?

Although both work in a similar way, using a GLP-1 receptor agonist, Mounjaro is not the same as Wegovy, which contains semaglutide. Mounjaro contains tirzepatide, which also works by reducing appetite and hunger levels, but it is the only one which is also a GIP receptor agonist. Both injectable weight loss medications are safe and effective when prescribed by a doctor and both are approved in the UK for weight loss.

How do I switch from Wegovy to Mounjaro?

If you wish to change from Wegovy to Mounjaro, you should speak to a doctor, who will explain when it’s safe to make the switch and how. There has to be a period of two months between stopping one and starting the other. Once you’ve switched, you’ll start taking Mounjaro on the lowest dose of 2.5mg.

How should I store Mounjaro?

Mounjaro pens should be stored in a fridge at a temperature of between 2 °C to 8 °C before use. Once they are opened, pens can either be stored in the fridge or away from direct sunlight in a cool, dark place -always at a temperature of below 30 ºC. Used pens should be discarded no later than 30 days after they have been first used.

Don’t store Mounjaro in a freezer, as if it gets too cold, the medication inside the pen could freeze and cannot be used, even if defrosted. As with any medication, keep it out of the reach of both children and vulnerable adults.

What happens if I stop taking Mounjaro?

Once you stop taking Mounjaro, the effects will begin to wear off, which means you will start feeling hungry more often again. If you were taking Mounjaro in order to regulate blood sugar, it is likely to return back to the same level as before. Always speak to your doctor before stopping Mounjaro, as they may ask you to slowly reduce the dose rather than stopping abruptly.

When Mounjaro is stopped too early, any weight you’ve lost may be put back on. It’s always advisable to speak to your doctor if you experience side effects and keep to the dosing schedule, as they can recommend you remain on the lower dose for longer.