Mounjaro® and Wegovy® are injected under the skin in one of the three approved Mounjaro injection sites — which are the same for Wegovy: the stomach, the thigh or the upper arm — and effectiveness is comparable across all three. So the real question isn’t “where”, it’s “how to alternate”: changing your injection spot from week to week is the simple habit that prevents most local reactions. Here are the official rules and the habits that make rotation easy.
The three official areas
The SmPCs of both treatments list the same subcutaneous injection sites:
- The abdomen — the most popular area, practical and easy to reach. Stay clear of the belly button (the instructions for use recommend about 5 cm / 2 inches) and vary your spots.
- The thigh — front of the thigh, upper and outer part.
- The upper arm — back of the arm; easier when someone can help you.
A reassuring point confirmed by the product information: you can switch areas freely, with no dose adjustment whatsoever. Stomach this week, thigh the next: the treatment works the same way.
Why rotate at all?
Injecting in exactly the same spot every time eventually irritates the skin: redness, itching, small hard lumps. These local reactions are usually mild and temporary — and largely avoidable. The recommendation in the instructions is simple: use a different spot for each injection — either within the same area (a different point on the stomach each week) or by switching areas.
A simple, effective rotation: right side of the stomach → left side → right thigh → left thigh, then start again. With one injection a week, each side is only used about once a month.
The spots to avoid
Whichever area you choose, never inject:
- where the skin is red, tender, hardened or bruised;
- into a scar, a mole or damaged skin;
- through clothing;
- and, on the abdomen, too close to the belly button.
One reminder that matters: these pens inject under the skin, never into a muscle or a vein — the short pen needle is designed exactly for that, no aiming required.
“I can’t remember where I injected last week”
That’s the one real problem with rotation: a week has passed, and last week’s spot is a distant memory.
The Doza app settles it: each time you log a dose, you note the site in one tap, and the app shows you where each area stands, pointing out the least recent one — your injection reminder can even whisper the next area in the rotation. The official sources (your treatment’s SmPC) are one tap away from the logging screen.
FAQ — injection sites
What is the best place to inject Mounjaro or Wegovy?
There isn’t one: stomach, thigh and upper arm are equivalent in effectiveness according to the product information. The best site is the one you rotate regularly, where the skin is healthy.
Do I need to change sites for every injection?
Yes, that’s the recommendation in the instructions: a different spot for each dose, within the same area or in another one. It limits local reactions (redness, lumps).
Can I switch from stomach to thigh without changing the dose?
Yes. The SmPCs state it explicitly: changing the injection site requires no dose adjustment.
Is injecting in the thigh less effective?
No. The three approved areas give comparable exposure to the medication — which is exactly why the product information treats them as interchangeable.
What if an area becomes red or hardened?
Avoid injecting there again until it looks and feels normal, and continue your rotation elsewhere. If the reaction persists, spreads or comes with other symptoms, show it to your doctor or pharmacist.
Sources: Wegovy® SmPC — EMA · Mounjaro® SmPC — EMA (sites: abdomen, thigh, upper arm; site changes need no dose adjustment; rotation recommended in the instructions for use). General information only: your pharmacist can demonstrate the technique when dispensing.