Medicines like Mounjaro are in pretty high demand right now. That’s because they work very well to support weight loss—better than diet and exercise changes alone, in fact—when taken as a weekly injection.
If you’re thinking of using Mounjaro, you might be especially curious about that last part: how am I meant to inject it?
Using an injector pen might feel daunting if you’ve never done it before. But we want to reassure you that the process is actually quite straightforward, though there are some steps you’ll need to follow. We’ve laid them out below.
You can also check out the video below, where Voy clinician Eve Agwuncha guides you through the process step by step.
What is Mounjaro?
First things first: Mounjaro is a medicine used for weight loss, that’s taken alongside healthy changes to diet and exercise.
It works by mimicking the effects of GIP and GLP-1, two “hunger” hormones that are naturally released when you eat. These actions slow down digestion to make you feel fuller, and reduce your appetite and cravings.
Mounjaro injection sites
Mounjaro is a subcutaneous injection—meaning that it should be injected into the fatty tissue just under your skin, rather than a vein or muscle.
You can inject it into your stomach, thigh, or the back of your upper arm.
So, which site should you pick? None are “better” than another, so you can use whichever you prefer. However, some people find injecting in the stomach easier. You might find it helpful to ask a family member or friend to help you when injecting in the upper arm.
Why do I need to use different injection sites?
You can use the same area of your body from week to week, so long as you inject into a different spot each time.
Because if you inject into the same spot again and again, it can cause fatty tissue to build up under the skin. This makes it harder for the medicine to be absorbed, which means you might not be getting your full dose. Injecting at a different spot each time will also reduce the chances of irritation at the injection site.
Where to inject Mounjaro
Stomach
You can inject Mounjaro into your stomach, at least 5cm away from your belly button.
Thigh
Another option is to inject Mounjaro into the front of your thighs.
Upper arm
Or you can inject Mounjaro into the back of your upper arm. Here, you’d have to get someone else to do the injection for you.
Preparing for a Mounjaro injection
There’s a bit of prep work you need to do before using the pen.
Read the leaflet
We know it sounds obvious, but first, make sure you read the instructions carefully. There should be a leaflet that came with the pens: find it, read it, make sure you understand it.
Wash your hands
Next, give your hands a thorough wash with soap and water.
Check the dose and pen
Take the pen out of the fridge (unused Mounjaro pens should always be kept in the fridge—never the freezer) and check it. You should only use it if:
- The dose is correct
- The medicine hasn’t expired
- The pen hasn’t been damaged
- The medicine isn’t cloudy or discoloured (Mounjaro should be colourless or slightly yellow) and doesn’t have any bits floating in it
- The medicine hasn’t frozen
If you’re good to go on all of the above, you can move on to the next step.
How to inject Mounjaro
Okay, it’s time to do the injection—we know you’ve got this. Carefully follow the steps below.
Get the pen ready
1. Clean the inner seal
Take the cap off the pen and wipe the red inner seal with an alcohol swab.
2. Ready the needle
Next, attach the needle to your pen. Take a needle head and pull off the paper tab at the back. Then, push it onto the pen and twist until it’s tight.
Once the needle head is secure, you can remove both the inner and outer shields protecting the needle. Don’t throw away the outer shield, though—you’ll use it later. The inner shield can go into your regular household rubbish.
Heads up: always use a new needle for each injection. This helps prevent infection and keeps the needles from getting blocked.
3. Prepare the dose
The small window at the bottom of the pen is called the dose window.
Slowly turn the knob at the end of the pen until you hear two clicks and a long line is shown in the dose window.
Then, hold the pen upright, so the needle is pointing to the ceiling. Tap the cartridge (the bit below the needle you see in the picture) gently. This will allow air bubbles to collect at the top.
Priming the pen - final preparations
You then need to check that the pen is in good working order.
Push the dose knob in until it stops and hold it, then slowly count to five. You should see a “0” in the dose window and a tiny drop of liquid coming out of the needle. This means that the pen is primed and ready for use.
If you don’t see any medicine come out, go back to step 3. You can do this twice if you need to. After that, if there still isn’t any liquid coming out, switch pen needles and start the whole process again. And if you still don’t see any liquid after that, contact us and we’ll help you.
Injecting Mounjaro using the pen
Turn the dose knob until a “1” comes up in the window. That means that your dose is loaded up and ready to go.
Pinch your skin and insert the needle through the fatty layer. Press the dose knob until it stops. Again, count to five slowly. When the dose window shows “0”, you’ve taken your full dose. Don’t remove the pen until you see the zero.
Take the pen out. That’s it, all done!
Don’t see the zero? It should show when the injection is finished. First, put the needle back in without turning the dose knob. If there’s still no zero, get in touch with us—don’t try to start over or give yourself another dose. This could put too much medicine in your system, which might make you feel sick.
After your injection
Storing Mounjaro safely
Carefully put the outer needle shield back onto the pen. Unscrew the capped needle head and put it into a sharps container. This is important, because if you store the pen with the needle attached it might leak or become blocked.
Pop the outer pen cap back on until your next injection. You can store used pens in the fridge or at room temperature (up to 30 degrees Celsius).
How do I know if I injected Mounjaro correctly?
What you see on the dose window shows whether you’ve done the injection right.
Before you inject Mounjaro, there should be a “1” in the dose window. This means that the dose is loaded up correctly and that you can use the pen.
When you inject the pen and the window shows “0”, it means that you’ve received the full dose.
If you have a reaction after using Mounjaro
You might experience some side effects when using Mounjaro, like nausea or diarrhoea. But for most people, symptoms are mild and go away on their own. You can reduce the chances of side effects by undertaking self-care measures like avoiding trigger foods, eating little but often and drinking plenty of water. Around one in ten people might get some itching, pain, or redness around the injection site.
It’s normal for there to be a drop of blood on your skin right after your injection. If that happens, press lightly onto the injection site with a cotton ball or some gauze. Try not to rub it.
If your symptoms don’t go away or are becoming a problem, check in with your doctor.
Reducing pain after injecting Mounjaro
Some people find that their injection site hurts after using Mounjaro. Here, as suggested above, you could try applying gentle pressure to that spot. It sounds simple, but scientific research shows that this can help to reduce pain.
Applying an ice pack to the sore area is also an option and you can also use over-the-counter painkillers like paracetamol or ibuprofen. Should the pain stick around or get worse, ask your doctor for advice.
Your next steps
We get that starting out with Mounjaro feels like a big step—in many ways, it is. Deciding to try a new medicine isn’t something done lightly.
But really, your weight loss journey is a series of little steps, done again and again and again. It’s about building habits that last: you’ll get the most out of Mounjaro when you use it for at least a year.
And we’re here to cheer you on at each stage of that journey. In our weight loss programme, you can get support from our team of experts plus weekly medication, and access to our coaching app to track your progress. Fill out this short form to find out if it’s right for you, it won’t take more than a few minutes.
FAQs
Does the Mounjaro injection hurt?
There isn’t much research specifically looking at whether Mounjaro injections hurt, but in clinical trials, around 3% of people using Mounjaro had an injection site reaction—which could include pain.
Research done on similar weight loss medications taken via injector pens, like Wegovy, found that injection pain was mostly mild or non-existent.
Mounjaro uses a very thin, short needle that delivers a small volume of liquid—0.6ml per dose. These factors are all thought to make injections less painful.
Can I inject Mounjaro in the same spot?
For the reasons we’ve explained above, we’re afraid the answer is no. Injecting into the same spot repeatedly can cause side effects like pain, irritation or swelling.
What’s the best time of day for injecting Mounjaro?
You should take Mounjaro on the same day every week, but it doesn’t matter which time of day you do it.
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³Eli Lilly. “Product Monograph Including Patient Information”. Eli Lilly. pi.lilly.com/ca/mounjaro-ca-pm.pdf Accessed 14 Nov. 2024
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