Where to Inject Mounjaro: Sites, Rotation & Step-by-Step Guide
You've got your Mounjaro pen in hand, the cap is off, and now you're staring at your stomach thinking — where exactly am I supposed to put this?
You're not alone. It's one of the most common questions we hear from people starting tirzepatide, and it matters more than you might think. Where you inject doesn't just affect comfort, it can influence how well the medication absorbs, whether you bruise, and how your body tolerates treatment over time.
At a glance
- Mounjaro (tirzepatide) can be injected into three areas: the abdomen, front of the thighs, or back of the upper arms
- The abdomen tends to offer the fastest, most consistent absorption — most patients find it the most comfortable too
- You should rotate your injection site each week to prevent skin irritation and hard lumps (lipohypertrophy)
- Always inject into subcutaneous fat, not muscle — a 90-degree angle into a pinched fold of skin is the standard technique
- If you're on blood thinners or bruise easily, the thigh often works better than the stomach
The three Mounjaro injection sites
Mounjaro is a subcutaneous injection — it goes into the layer of fat just beneath your skin, not into muscle or vein. The medication's prescribing information from Eli Lilly approves three areas:
Your abdomen
This is where most people start, and for good reason. The stomach area has a generous layer of subcutaneous fat in most people, which makes it easier to get the technique right.
The key rule: stay at least 5cm (about two inches) away from your belly button. The tissue immediately around the navel is denser and has different blood supply, which can affect absorption and cause more discomfort. You've got the entire area below your ribs and above your hips to work with.
A few specifics worth knowing. The lower abdomen (below the navel line) tends to have slightly more subcutaneous fat for most people, which can make the injection more comfortable. Avoid any areas with scars, stretch marks, or visible veins — they'll absorb differently and bruise more easily.
The front of your thighs
Your second option, and a good one, particularly if you're lean around the middle or find stomach injections uncomfortable. Use the top, outer portion of the front of your thigh, roughly in the middle third between your knee and hip.
The thigh has slightly different absorption characteristics than the abdomen. Studies on subcutaneous injections generally show marginally slower absorption from the thigh compared to the abdomen, though with tirzepatide's once-weekly dosing this difference is clinically insignificant. What matters more is consistency — pick sites you can use reliably each week.
One practical advantage of the thigh: it's easier to see exactly what you're doing, which can help when you're still getting used to the pen.
The back of your upper arms
The upper arm works well, but it's difficult to inject yourself here. You need to reach the fleshy area at the back of the arm, roughly between your shoulder and elbow, and most people can't comfortably pinch the skin and operate the pen one-handed.
If you have a partner, family member, or housemate who's willing to help, the upper arm is a perfectly good site. But if you're doing this solo, you'll likely find the abdomen and thighs far more practical.
Which injection site is best?
The one you'll use consistently.
That said, if we're being specific: for most patients, the abdomen offers the best combination of comfort, ease of access, and absorption reliability. There's a reason it's the first recommendation in most clinical guidance.
But here's what we'd encourage you to think about: your body is yours, and it's different from everyone else's. Someone with very little abdominal fat might find the thigh significantly more comfortable. Someone who bruises easily on their stomach might get better results on their outer thigh.
A few situations where one site may work better than another:
If you bruise easily or take anticoagulants — the front of the thigh tends to cause less bruising than the abdomen for many people. The skin is thicker, and there's generally less superficial blood vessel density. Worth trying if you're getting marks every week.
If you're very lean — look for wherever you can most easily pinch a fold of fat between your thumb and forefinger. If you can't get a good fold on your stomach, the thigh will be more comfortable.
If you have skin conditions like eczema or psoriasis — avoid injecting into any area with active flare-ups. Inflamed skin absorbs medication unpredictably and you'll likely get more irritation.
How to rotate your injection sites properly
Site rotation isn't optional. Injecting into the same spot week after week can cause lipohypertrophy — hardened lumps of fatty tissue under the skin. These aren't just cosmetically annoying; they affect absorption. Medication injected into lipohypertrophic tissue absorbs erratically, which means your dose may not work as effectively.
The rule is straightforward: each weekly injection should go into a different spot, at least 2-3cm away from where you injected last time. You can stay within the same general area (say, the abdomen) but move the exact location around.
Here's a practical four-week rotation that works well:
- Week 1 — right side of abdomen, below the navel
- Week 2 — left side of abdomen, below the navel
- Week 3 — right thigh, outer front
- Week 4 — left thigh, outer front
- Then repeat
Some people prefer a simpler two-site rotation — alternating between left and right abdomen each week. That's fine too, as long as you're spacing the exact injection point by a few centimetres each time.
A tip that helps: keep a simple note on your phone. Just jot down "left stomach" or "right thigh" after each injection. It takes three seconds and saves you trying to remember the following week. Some people use a Mounjaro app; others just add it to their calendar entry.
Step-by-step: how to inject Mounjaro
If this is your first time, take a breath. The Mounjaro KwikPen is designed to be straightforward, and the needle is very fine — most people describe it as a slight pinch rather than real pain.
Before you start:
Take the pen out of the fridge 30 minutes beforehand. Cold medication stings more on injection and can feel uncomfortable as it enters the tissue. Let it reach room temperature naturally — don't try to warm it with hot water or a microwave (this can damage the tirzepatide).
Check the pen. Look at the solution through the window. It should be clear and colourless to slightly yellow. If it's cloudy, contains particles, or has changed colour, don't use it.
The injection itself:
Wash your hands with soap and water.
Choose your injection site and clean the area with an alcohol swab. Let it air dry completely — injecting through wet alcohol stings unnecessarily.
Remove the pen cap. You'll see the grey base cap — twist it off and pull it straight away from the pen. This exposes the needle.
Pinch a fold of skin at your chosen site. Use your thumb and forefinger to lift about 2-3cm of skin and fat away from the underlying muscle. This ensures the needle reaches subcutaneous tissue, not muscle.
Insert the needle at a 90-degree angle to the skin. Push it in fully — the needle is short and designed to reach the right depth in most body types.
Press and hold the injection button. You'll hear a click. Keep the pen pressed against your skin and hold for the full 10 seconds — you'll hear a second click when the dose is complete. The grey plunger will be visible in the window.
Remove the needle straight out. Don't rub the site — this increases bruising. If there's a small drop of blood, press gently with a clean cotton pad for 10-20 seconds.
That's it. The whole process takes under a minute once you've done it a couple of times.
Dealing with bruising, lumps and discomfort
Some bruising is normal, especially in the first few weeks while you're perfecting your technique. Small bruises that fade within a few days aren't a concern.
To minimise bruising:
Let the alcohol swab dry completely before injecting. Wet alcohol disrupts the skin surface and increases bleeding. Ice the area for 2-3 minutes before injecting if you're prone to bruising — this constricts the superficial blood vessels. Don't rub the injection site afterwards. And check your technique: are you going in at a true 90-degree angle? Angled needle entry damages more tissue.
If you're finding hard lumps under the skin, that's lipohypertrophy — a sign you're injecting in the same spot too often. Stop using that area entirely for at least 4-6 weeks and rotate more diligently. The lumps will usually resolve on their own, but mention them to your prescriber because they may affect how well your current dose is absorbing.
If you notice redness, swelling or warmth that's getting worse rather than better over 24-48 hours, or if you develop a fever, contact your GP or pharmacist. Injection site infections are rare with proper technique, but they do happen and need prompt treatment with antibiotics.
If you're on blood thinners (warfarin, apixaban, rivaroxaban, or even daily aspirin), expect more bruising than average. This is normal. The thigh is generally a better option as it tends to produce smaller bruises. Apply gentle pressure for a full 30 seconds after removing the needle, rather than the usual 10-20. And never inject into an area that's already bruised from a previous dose.
What to do when things go wrong
The medication leaks out after injection. A tiny droplet at the injection site is normal — this is residual medication in the needle, not your full dose. If you see a visible stream or the plunger didn't fully advance, you may not have received the complete dose. Don't re-inject — note what happened and contact your prescriber for advice.
You injected into muscle instead of fat. If the needle went in without a skin pinch and you felt deeper, sharper pain, you may have hit muscle. The medication will still absorb, but potentially faster than intended, which can increase side effects like nausea. It's not dangerous. Make sure to pinch properly next time.
You forgot to let the pen warm up. Cold injection just means more discomfort — it doesn't affect the medication itself. You'll be fine, but try to remember next week. Setting a phone reminder 30 minutes before your injection time helps.
You noticed blood in the pen window. This is uncommon but harmless — it means the needle nicked a small blood vessel. The dose is still effective. Use a fresh pen for your next injection as normal.
You missed your injection day. Mounjaro should be taken on the same day each week. If you miss your day, inject as soon as you remember, as long as it's within 4 days of your scheduled dose. If more than 4 days have passed, skip that dose entirely and take the next one on your regular day. Don't double up.
How to dispose of used pens safely
Used Mounjaro pens contain a needle and traces of medication — they can't go in your regular household bin.
You need a sharps container. Your pharmacy should have provided one when you started treatment, but if not, you can request one free of charge from most pharmacies or your local council. Yellow sharps bins are the standard in the UK.
Never put loose pens or needles in a plastic bag, cardboard box or directly in the bin. This is a safety issue for anyone handling your waste.
The bottom line
Mounjaro goes into the fat layer beneath your skin — the abdomen, front of the thighs, or back of the upper arms. For most people, the stomach is the most comfortable and practical starting point, but your thighs are an equally good option, especially if you bruise easily.
The single most important thing? Rotate your site each week. Keep a quick note on your phone, follow a simple pattern, and you'll avoid the lumps and absorption issues that come from injecting in the same place repeatedly.
If you're just starting Mounjaro and want clinical support from a team that actually follows up, start a consultation with heySlim — we'll make sure you're set up properly and check in as you go.
Frequently asked questions
Can I inject Mounjaro into my belly button area?
No — stay at least 5cm (two inches) away from your navel. The tissue around the belly button is denser and has a different blood supply, which affects absorption and tends to be more painful. Use the wider area of your abdomen below the ribs and above the hips.
Does it matter what time of day I inject Mounjaro?
Not clinically — tirzepatide works over the full week regardless of when you take it. That said, many patients prefer injecting in the evening so that any initial nausea (which is most common in the first few weeks) happens while they're asleep. Pick a time that fits your routine and stick with it.
What's the best injection site to avoid nausea?
Nausea from Mounjaro is a systemic side effect caused by the medication itself, not by the injection site. Changing where you inject won't reduce nausea. If nausea is bothering you, speak with your prescriber about dose titration speed — going up more slowly often makes a significant difference.
Can I inject through clothing?
No. Always inject into clean, bare skin. Injecting through fabric increases infection risk and can affect how the needle enters the tissue. It only takes a moment to lift your top or adjust your clothing.
How do I know the injection worked?
After pressing the injection button and holding for 10 seconds, you'll hear a second click and see the grey plunger visible in the dose window. This confirms the full dose has been delivered. If the plunger hasn't moved or you didn't hear the second click, the dose may not have been fully administered — contact your prescriber.
This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before starting any treatment.