Where do you inject semaglutide, and how often should you rotate?

What do the labels say?

The Wegovy prescribing information says to inject subcutaneously in the abdomen, thigh, or upper arm, and to rotate injection sites with each dose.¹ The Ozempic label names the same three regions and adds a practical rule: use a different injection site each week when injecting in the same body region.² So returning to the abdomen every week is fine; returning to the same square inch of it is what the label is steering you away from.

The tirzepatide labels, Zepbound and Mounjaro, agree on the regions and the rotation, with one wording difference worth noticing. They say to inject in the abdomen or thigh, or to have another person inject in the back of the upper arm.³⁴ The back of the arm is awkward to reach with your own hands, and the label treats it as a site for a helper.

Subcutaneous means into the fat under the skin. None of these labels describes injecting into muscle, and the regions they name are the ones where that fat layer is easiest to find.

Does the site change how much you absorb?

Not according to the pharmacology sections. The semaglutide label states that similar exposure was achieved with subcutaneous administration in the abdomen, thigh, or upper arm,¹² and the tirzepatide label says the same of its molecule.³ Claims that one site absorbs better or faster than another, which circulate widely, are not supported by the labels of either drug.

That matters for how you think about rotation. If the arm gave less drug than the abdomen, rotating would change the dose from week to week. The labels say it does not, which leaves the real reason to rotate.

Why rotate at all?

Because repeated injection into one spot changes the tissue, and the evidence for that comes from insulin, where people inject daily and the problem is easy to study. The 2016 FITTER recommendations, written and vetted by 183 diabetes experts from 54 countries, describe lipohypertrophy, a thickening of the fat under the skin, as a frequent complication that distorts insulin absorption, and state that injections should not be given into these lesions and that correct site rotation will help prevent them.⁵

A Spanish study put numbers on it. Of 430 insulin-injecting outpatients examined by a diabetes nurse, 64.4% had lipohypertrophy. Among those who rotated sites correctly, only 5% had it, while 98% of those who had it either did not rotate or rotated incorrectly. Reusing a needle more than five times raised the risk as well.⁶

A weekly GLP-1 injection is a very different schedule from several insulin injections a day, and the GLP-1 trials did not study lipohypertrophy. What the labels do report is injection site reactions: 3.2% of Mounjaro patients against 0.4% on placebo,⁴ and 6% to 8% on Zepbound against 2% on placebo.³ Rotation is the label's standing instruction for both drugs, and the insulin evidence is the clearest picture of what happens when it is ignored.

How do you keep track of rotation?

Memory is the usual method and the usual failure. A site used three weeks ago looks exactly like one used three days ago, which is why the question people actually type is "where did I inject last time?"

Protocol Her answers it with a body map. Each injected dose is logged to one of ten sites: left or right abdomen, thigh, arm, glute, or flank. The map shades each site by how often it has been used in the last 30 days, so a site that is carrying more than its share is visibly warmer, and once any dose has been logged it marks the site that has gone longest without use as the suggested one. Doses taken by a non-injected route, nasal, oral, or topical, store no site and leave the map alone. The next-dose card on the home screen also shows the site of the last logged dose for that compound, so the answer to "where did I inject last time?" is on the first screen you open.

The map offers more regions than the semaglutide label names, because the app tracks other compounds whose instructions differ. Which regions apply to a given product is the label's call, not the map's. If a site reacts, the side-effect sheet has an "Injection site reaction" chip for a welt, redness, a nodule, itching, or bruising at the site, logged with a severity and tied to the dose it followed, so a site that keeps reacting shows up in the record rather than in hindsight. Both the semaglutide guide and the tirzepatide guide cover how each compound is tracked, and the syringe units page covers what the marks on the barrel mean.