Learning how to inject Mounjaro can feel daunting, especially if you've never given yourself a shot before. The good news? Mounjaro comes as a pre-filled pen, designed to make things as straightforward as possible.

You inject Mounjaro once a week under your skin, usually in your abdomen, thigh, or upper arm. With a bit of practice, it becomes a quick and manageable part of your week.

We get it. Taking that first step brings up questions. Where do you inject, exactly? What if you mess up? How do you keep the pen safe between doses?

This guide covers what you need to know to inject Mounjaro safely and confidently. Whether you're starting treatment after an online consultation with a private provider or through the NHS, the injection technique is the same. From prepping the site to what happens after you press the button, let's walk through it together.

Key takeaways

Mounjaro is a once-weekly injection you give under the skin with a pre-filled pen.

You can inject in your abdomen, thigh, or upper arm, but switch spots each week.

Good prep and technique lower side effects and help the medicine work its best.

If you experience severe stomach pain, ongoing vomiting, or signs of allergic reaction, seek medical help immediately.

Understanding Mounjaro and its uses

What is Mounjaro and how does it work?

Mounjaro is a prescription drug with tirzepatide as the active ingredient. You'll need an assessment with a healthcare professional who will check your eligibility and decide whether it's suitable for you based on your medical history, current medications, mental health, and weight-related health conditions.

A person holding a Mounjaro pen thoughtfully, surrounded by icons representing the dual hormone action – appetite signals going to the brain, a stomach, and a pancreas.

Mounjaro mimics two natural gut hormones, not just one. It activates both GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) receptors in your body.

What does this actually do?

Tells your pancreas to pump out more insulin when your blood sugar goes up
Reduces how much sugar your liver makes
Slows down how fast food leaves your stomach
Sends signals to your brain so you feel fuller, longer

By reducing cravings and promoting appetite suppression, Mounjaro helps you naturally consume fewer calories without feeling constantly hungry. It also affects your metabolism, helping your body process food more efficiently. These combined effects support weight loss when paired with healthy eating and regular physical activity.

This dual action, on both GLP-1 and GIP, is what sets Mounjaro apart from meds like semaglutide, which only works on GLP-1. That "twin hormone" approach seems to deliver stronger results for a lot of people.

You inject Mounjaro once a week with a pre-filled pen. Most doctors start you on a low starting dose (2.5mg weekly) and gradually increase towards your maintenance dose over several weeks. You'll typically increase every 4 weeks towards your target maintenance dose (5mg, 7.5mg, 10mg, 12.5mg, or 15mg depending on your response and tolerability). This helps your body adjust and reduces side effects.

Who can benefit from Mounjaro injections?

Mounjaro isn't for everyone. You'll need a prescription from a healthcare provider who can decide if it's right for you.

For type 2 diabetes:

Mounjaro often helps people who haven't hit their blood sugar goals with other meds. It's especially handy if losing weight would help control your diabetes. Most folks use it along with diet and exercise tweaks, sometimes with other diabetes drugs.

For weight management:

Mounjaro is approved for the management of obesity in adults with obesity who meet specific criteria. It's licensed for adults with a BMI (Body Mass Index, a measure of weight relative to height; you can check yours using the NHS BMI calculator) of 30 or more, or 27 or more with a weight-related condition. However, NHS access is more restricted.

NICE recommends Mounjaro for adults with a BMI of at least 35 and at least one weight-related health condition (also called a comorbidity). The current NHS rollout prioritises people with a BMI of 40 or more (37.5 for certain ethnic groups) plus four or more weight-related conditions, including type 2 diabetes, hypertension, dyslipidaemia (abnormal blood fat levels), obstructive sleep apnoea, and cardiovascular disease. Private clinics may offer wider access if you meet the drug's licensed criteria.

Mounjaro works best as part of a broader approach that includes building healthy habits around nutrition and exercise.

Who shouldn't use Mounjaro:

Mounjaro isn't suitable if you're pregnant, planning to become pregnant, or breastfeeding. You shouldn't use it if you have a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN2), or if you have a history of pancreatitis. Your prescriber will assess your full medical history before recommending treatment.

If you use oral contraceptives, be aware that Mounjaro may reduce their effectiveness. Use additional barrier contraception (such as condoms) for 4 weeks after starting treatment and for 4 weeks after each dose increase.

Mounjaro as a weight loss and diabetes treatment

Clinical studies show big results for both weight and blood sugar. In the SURMOUNT-1 clinical trial, people taking Mounjaro for weight loss lost an average of 15% to 22.5% of their body weight over 72 weeks (about 18 months), depending on the dose. That's significantly more than lifestyle changes alone.

Weight loss with Mounjaro includes both fat and some lean mass (muscle). To help preserve muscle during weight loss, many healthcare providers recommend increasing your protein intake to around 1.0–1.2g per kilogram of body weight daily and including some resistance exercise.

For type 2 diabetes, Mounjaro brings blood sugar levels down effectively. Many people achieve better HbA1c levels (a measure of average blood sugar over 2-3 months) than with their previous treatments.

But here's the thing: Mounjaro works best for weight loss when you combine it with lifestyle changes. You'll probably eat less because it curbs your appetite, but you still need to focus on good food and regular movement.

Common side effects to expect:

Nausea or feeling a bit sick (typically improves within 2–4 weeks on a stable dose)
Changes in bowel habits
Less appetite
Sometimes a bit of stomach discomfort

Most side effects are mild and tend to fade as your body adjusts. Starting low and going up slowly helps keep things manageable.

If you stop taking Mounjaro, your appetite will likely return to what it was before treatment, and weight regain is common. GLP-1 weight loss treatments don't "cure" obesity. They help manage it while you're taking it. This is why building eating and exercise habits alongside the medication is so important.

Contact your doctor right away if you have severe stomach pain, ongoing vomiting, or signs of an allergic reaction. These are rare, but they need urgent attention.

Preparation before injecting Mounjaro

Getting ready for your Mounjaro shot doesn't have to be complicated. Gather your supplies, check your pen, and make sure you've got the right dose before you start.

Gathering supplies and essential equipment

Lay out what you need on a clean surface. Grab your Mounjaro pen (the KwikPen), a fresh pen needle, alcohol swabs, and a sharps bin.

Pick a spot that's well-lit and comfy, so you're not rushed. Store your Mounjaro pen in the fridge (2°C to 8°C), as recommended in the Mounjaro Summary of Product Characteristics, until you need it. Take it out about 30 minutes before your shot so it warms up a bit.

What you'll need:

Mounjaro KwikPen (for single-patient use)
Sterile pen needle
Alcohol swabs
Sharps disposal container
Clean, flat surface

An infographic showing the five essential supplies for a Mounjaro injection: the KwikPen, a sterile needle, alcohol swabs, a sharps container, and a clean flat surface.

⚠️ Important: Never share your Mounjaro pen with another person, even if you change the needle. Sharing pens can spread serious infections. Each pen is meant for single-patient use only.

Checking and handling the Mounjaro pen

Look over your pen before attaching the needle. Check the liquid through the cartridge holder. It should look clear and colourless. If you spot particles, cloudiness, or anything odd, don't use that pen.

Double-check the label to confirm you've got the right dose. The dose is printed on the pen. Make sure it matches your prescription.

Hold the pen gently but firmly. You'll see the dose knob at one end and the cartridge at the other. The pen's designed to be simple, and the patient information leaflet has detailed instructions with pictures.

Priming the pen and ensuring proper dose

Attach a new pen needle, then remove both the outer and inner needle caps. Hold the pen with the needle pointing up and tap the cartridge holder so air bubbles move to the top.

Turn the dose knob to select the priming dose (usually a tiny amount). Press and hold the injection button until you see a drop of liquid at the needle tip. That's your sign that the pen's working right.

Now dial your prescribed dose using the knob. The number appears in the window. Double-check it matches your script. If you go past your dose, just turn the knob back.

The pen's ready. Don't take the needle off yet or set the pen down where it might roll away.

How to inject Mounjaro: step-by-step instructions

Injecting Mounjaro yourself might feel intimidating the first time. But once you've done it, the steps start to make sense.

We'll go through choosing your injection spot, prepping your skin, giving the shot, and getting rid of the pen safely.

Selecting the correct injection site

Mounjaro is a subcutaneous injection, which means it goes into the fat layer just under your skin. You've got three main options: abdomen, upper thigh, or upper arm.

Your best Mounjaro injection sites:

Abdomen (stomach area): Most people say this spot is easiest. Just steer clear of the area within 5 cm of your belly button.
Upper thigh: The front or outer part works well if you're injecting yourself.
Upper arm: The back is suitable, but you'll need someone to help if you pick this spot.

A body diagram showing the three Mounjaro injection sites: abdomen (avoiding the area around the belly button), front of thigh, and back of upper arm.

Can I inject Mounjaro in the same spot every week?

No, you should rotate your injection sites to prevent lumps, scarring, or irritation. Try dividing your abdomen, thighs, and upper arms into sections, and wait at least four weeks before returning to the same spot. Always inject at least a finger-width away from your last injection site.

Cleaning and preparing the injection area

Before injecting, prep both your skin and the pen. Clean hands are a must. Wash with soap and warm water.

Take your Mounjaro pen out of the fridge about 30 minutes before your weekly injection. Room temperature makes the shot easier and more comfortable.

Check the pen again before use. Look through the window. The liquid should be clear and colourless. If you see anything off, like cloudiness or particles, don't use it.

Clean your chosen injection site with an alcohol wipe. Use a circular motion, starting at the centre and working outward. Let the area dry completely (about 10 seconds). Don't blow or fan it. Just give it a moment.

Administering the subcutaneous injection

Alright, time to inject. Take off the base cap from your Mounjaro pen. You'll spot the grey injection button. Don't press it just yet.

Hold the clear base flat against your cleaned skin at a 90-degree angle. The pen should sit flush against your skin.

Push the pen firmly until you can't press it down any further. Now, press and hold the grey injection button.

You'll hear two clicks. The first click means the injection's started. Keep holding the pen in place.

The second click means you're done, but don't pull the pen away yet. Count slowly to 10 while it stays pressed against your skin.

This helps you get the full dose. The viewing window will turn purple when it's finished.

Pull the pen straight off your skin. The needle retracts automatically back inside the pen.

Sometimes, you'll see a tiny drop of blood or liquid at the injection site. Totally normal.

A step-by-step process diagram showing the four key stages of administering a Mounjaro injection: remove cap, hold pen at 90 degrees, press and hold button until two clicks, count to 10 then remove.

Aftercare and proper disposal

If you see a bit of blood or clear liquid, just press a clean cotton ball or gauze pad gently over the spot. Don't rub it.

You might notice some redness or mild tenderness where you injected. Usually, that goes away in a few hours.

If the spot gets more painful, swollen, or hot, reach out to your doctor. Never reuse your Mounjaro pen. Each one is for single use only.

Drop the used pen straight into a sharps container. If you don't have one, a hard plastic bottle with a screw-top lid (like an empty laundry detergent bottle) works in a pinch.

Don't toss used pens in your regular bin. When your sharps container is about three-quarters full, check with your local pharmacy about disposal.

Many pharmacies will take sharps containers and handle safe disposal for free.

Safety, side effects, and tips for success

Mounjaro can cause reactions at the injection site, and you might run into other side effects as your body gets used to it. Knowing what could happen (and how to deal) helps you stay comfortable and get the best out of your treatment.

Managing common injection site reactions

Injection site reactions are pretty common when you start Mounjaro. You might spot some redness, swelling, or a little lump where the needle went in.

Usually, these clear up after a few days. Rotating your injection sites really helps. Don't use the same spot two times in a row.

If you did your left thigh last time, switch to your right thigh or maybe your stomach for the next one. It gives each spot a break.

Try holding a cold compress on the area for about 30 seconds before injecting. It can numb things a bit.

After you inject, another cold compress can bring down swelling or discomfort. If reactions stick around for more than a week or get worse, reach out to your healthcare provider.

Severe pain, spreading redness, or warmth around the site could mean infection. Don't ignore it.

Potential side effects and how to handle them

The most common Mounjaro side effects mess with your stomach. Nausea, vomiting, diarrhoea, and constipation can happen because the medication slows down how quickly food moves through your system.

Nausea tends to hit hardest in the first few weeks. Approximately 1 in 4 people experience nausea, particularly during dose escalation. Eating smaller meals throughout the day usually works better than three big ones.

Steer clear of greasy or spicy foods. Ginger tea or plain crackers can be lifesavers for a queasy stomach.

Constipation? More fibre and water can really help. Add veggies, fruit, and whole grains to your meals, and aim for at least 2 litres of water daily (the NHS Eatwell Guide recommends 6–8 glasses of fluid daily as a baseline).

Some people experience tiredness, particularly in the early weeks of treatment. This often improves as your body adjusts. Staying hydrated is important to help prevent dehydration, which can worsen fatigue and other side effects. If tiredness persists, mention it to your prescriber.

Mounjaro lowers blood sugar, especially if you're also on insulin or other diabetes meds. Watch for shakiness, sweating, confusion, or sudden hunger.

Keep glucose tablets or juice nearby, just in case. Your doctor might need to tweak your other medications.

Rapid weight loss can increase your risk of gallstones. Watch for symptoms like pain in your upper right abdomen, fever, or yellowing of your skin or eyes. If you notice these signs, contact your doctor promptly.

⚠️ Seek urgent medical help if you experience

Severe stomach pain that won't go away (possible pancreatitis)
Ongoing vomiting you can't control
Vision changes
Signs of allergic reaction (rash, swelling, difficulty breathing)
Symptoms of gallbladder problems (pain in upper right abdomen, fever, yellowing skin)

Tips for comfort and effective treatment

Let the pen warm up to room temperature before injecting. Cold medication stings more, so take it out of the fridge about 30 minutes before your injection time.

Inject slowly and steadily. If you rush, you'll probably feel more discomfort or end up with a bruise.

Press the button, count to ten, then pull the needle out. That way, you know you got the full dose.

Stay consistent with your schedule. Try to pick the same day each week for your shot.

Set a phone reminder if you need to. Missing doses or taking them late can bring back hunger and make the medication less effective. Nobody wants that.

Keep a diary of when you inject and jot down any side effects. This helps you notice patterns and gives your doctor real info between appointments.

Note what you ate before you felt sick, or which injection sites felt better. Sometimes those little details make a difference.

Store unused pens in the fridge between 2°C and 8°C. Never freeze them. That's important.

Once you start using a pen, you can keep it at room temperature for up to 21 days, according to the manufacturer's guidance. Makes life a bit easier, right?

Choosing the right provider

Injection technique is only one piece of the puzzle. Whoever you get your Mounjaro from also affects how confident you feel — clear instructions, easy access to a clinician when something doesn't feel right, and reliable supply all vary significantly between UK providers.