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Semaglutide is injected subcutaneously, meaning into the fat just under the skin, at one of three sites: the abdomen, the front of the thigh, or the back of the upper arm. All three work. Pick the one you can reach comfortably, and then move the exact spot each week.
That’s the whole answer, and the rest is mechanics. Everything below applies to tirzepatide too, since it uses the same route and the same three sites. If you’re on compounded semaglutide, your pharmacy insert has the details for your vial.
What each site is like to use
Abdomen. This is the default. It has plenty of fat under the skin, you can see what you’re doing, and you can pinch a fold with one hand. Stay at least two inches from your navel, and skip scars, moles, and anything still bruised from last time.
Front of the thigh. Sit down and inject into the top of your thigh, halfway between your hip and knee. It’s useful when the abdomen is off the table. The fat layer here is thinner on lean bodies, so if you can’t pinch much, the abdomen is more forgiving.
Back of the upper arm. It’s a standard site, but it’s awkward to do alone. Pinching and injecting the back of your own arm with one hand takes some contortion. It’s the site for people who have someone else give the shot.
At all three sites, the target is the fat layer, not the muscle. Needle and syringe details vary by product and pharmacy, so follow what ships with your prescription. The full technique, including drawing up a dose, needle angle, air bubbles, and disposal, is in our step-by-step injection guide. This article sticks to where.
Pick the site that’s comfortable
None of the three sites is ranked above the others, so choosing one is mostly about comfort. Pick based on lighting, your dominant hand, and which skin is least irritated this week. Sticking to one region forever is fine.
Same region every week is fine, but not the same spot
There’s one firm rule: change the exact injection spot each time. You can use your abdomen for years, but you shouldn’t use the same square inch of it twice in a row.
The reason comes from insulin research, since GLP-1 trials didn’t test it. Decades of daily insulin use showed that hitting the same patch of skin over and over causes lipohypertrophy. That’s rubbery, thickened fat that absorbs the drug unevenly. A weekly GLP-1 puts a fraction of that load on your skin: 52 injections a year, compared with more than a thousand for insulin. No one has tested rotation schedules for once-weekly drugs, and no one is likely to. But the mechanism carries over, and rotating costs nothing.
Here’s a pattern that takes no memory. Treat the area around your navel as four quadrants. Week 1 is upper right, week 2 lower right, week 3 lower left, and week 4 upper left. Each patch of skin sees a needle about once a month, and within a quadrant you still land an inch away from any mark you can see. On the thigh, the same logic works with right leg and left leg, upper half and lower half.
The real mistake isn’t picking the wrong quadrant. It’s slowly drifting back to the one spot that doesn’t sting. Some people find it early on and stay there without ever deciding to. If you can’t remember where you injected last week, you’re already doing it. Write the quadrant on the box.
What a normal site reaction looks like
A small red bump, a faint bruise, or an itch that fades within a day or two is normal. Site reactions are usually mild and local, and rotation does most of the prevention. What’s not normal is redness that spreads, skin that gets hotter or more painful over 48 hours, or swelling that grows instead of shrinking. That pattern deserves a same-day message to your clinician instead of a week of watching.
A photo helps, but only a useful one. Draw a pen line around the edge of the redness, write the date next to it, and photograph the whole thing in daylight. The line is the point, because it turns your next photo into a real comparison. Redness spreading past the line over 24–48 hours is the finding that changes what we do. A red patch on its own, with nothing to compare it to, tells us almost nothing.
The next step
Already injecting? Set your quadrant pattern this week, which is a ten-second decision you only make once. If your first dose is still ahead of you, read the injection guide from start to finish before you open the box. And if you haven’t started at all, the five-minute quiz checks whether you’re a candidate. A clinician reviews every intake within 24 hours.
