Where do you inject weight loss shots — and does the site actually matter?

The myth worth correcting first: any spot on your body will do

People sometimes assume that because these are self-administered injections, the location is flexible, anywhere with a bit of flesh will work. That is not quite right. Both Mounjaro and Wegovy are subcutaneous injections, meaning the medicine goes into the thin layer of fatty tissue that sits beneath the skin but above the muscle. Inject too shallow and you risk a skin reaction; go deeper into muscle and the absorption rate changes, and it hurts more. The licensed sites for both medicines are the abdomen, the outer thigh, and the upper outer arm. Stick to those three. Within the abdomen, keep at least a couple of centimetres away from your navel. The upper arm site is the one most people need a hand with at first, if you are injecting there alone, a mirror or a firm surface to brace against helps considerably.

Rotation is not optional. Using the same spot every week gradually hardens the tissue underneath (a process called lipohypertrophy) and hardened tissue absorbs medicine less predictably. A simple rule is to work around each site before repeating: for the abdomen, move the injection point a few centimetres from last week's spot and work around the clock. The how GLP-1 injections work guide covers the mechanics behind absorption in more detail if you want the fuller picture.

What each approved site actually looks like in practice

The abdomen is the site most people start with. Aim for the area of the stomach between your hip bones, below the ribs and above the groin, avoiding the strip directly around your navel. Pinch the skin lightly if the area is lean, but with the pre-filled pens used for Mounjaro and Wegovy you do not need to pinch in most cases, hold the pen firmly against the skin, press, and the pen handles the rest.

The outer thigh is a good alternative, especially if your abdomen feels tender after a recent injection. Use the front or outer side of the thigh roughly halfway between the hip and knee. Avoid the inner thigh, where skin is thinner and the area closer to larger vessels.

The upper arm requires a bit more preparation when self-injecting. The target is the outer, fleshy part of the upper arm, think roughly where a seasonal flu jab lands. Some patients find it easiest to sit the back of their arm against a wall or chair arm to keep it still.

Alcohol wipes clean the skin before each injection. If you need a reliable supply, alcohol swabs are available alongside your treatment. Let the area dry fully before injecting, wet skin stings more and can affect how the pen adheres.

Changing the needle and disposing of it safely

Mounjaro's KwikPen uses a separate needle that attaches before each dose and should be removed and discarded immediately after. Using the same needle twice is a common shortcut that blunts the tip, increases discomfort, and raises the risk of blocked delivery. Fresh needles matter, especially as the weeks go on and the doses increase. If you are running low, compatible pen needles can be ordered so you are never making do.

Used needles and sharps go into a proper sharps bin, not a household bin or recycling. Many GP surgeries and some community pharmacies accept full sharps bins for disposal. A 1-litre sharps container is the standard size for home use and keeps everything contained between disposal trips. Some people find it helpful to keep the bin on the worktop next to the fridge during their Sunday evening routine, once it becomes a habit, the whole process takes under two minutes.

For a broader look at how many injections are involved over the course of treatment, the guide on injection frequency covers the weekly schedule and what to expect at each stage. The overview of weight loss injection options is worth reading if you are still comparing medicines.

When to seek help and what to watch for at injection sites

Minor redness or a small raised bump immediately after injecting is common and usually settles within an hour or two. More persistent reactions (lumps that stay for days, significant bruising, or any sign of infection such as warmth, swelling or discharge) should be discussed with your prescriber promptly. Do not keep injecting into an area that looks or feels wrong.

The most frequently reported side effects of GLP-1 medicines are gastrointestinal rather than site-related: nausea, loose stools, constipation, and burping are common, particularly after a new dose, and generally ease within a week or two. The NHS tirzepatide medicines page lists the full side-effect profile for Mounjaro, and the MHRA's Yellow Card scheme allows you to report any reaction you are concerned about, including anything at the injection site. Reporting helps the regulator track real-world safety across thousands of patients.

If you are not yet on treatment and want to understand your options, the guide on where to access weight loss injections in the UK explains the NHS and private routes. If you would like more detail on the clinics, pharmacies, and online services available to you, our page on where to go for weight loss injections walks through the main routes so you can choose what suits your circumstances. When you are ready to find out whether you are clinically suitable, check your eligibility with our prescribers, the consultation is free and reviewed the same day.