The short answer is the abdomen, the thigh and sometimes the upper arm, but your product’s label decides. Each FDA-approved peptide label names its own sites. They overlap, and they do not all match. Every one also says to rotate.
This page lists what the labels say. It is not a guide to injecting any product your prescriber has not shown you how to use. Research-only compounds such as BPC-157 have no label at all.
What each label names
The tirzepatide label for ZEPBOUND says to inject under the skin of the abdomen or thigh [1]. Another person may inject into the back of the upper arm. The label says to rotate sites with each weekly dose.
The tesamorelin label for EGRIFTA SV is narrower [2]. It names the abdomen only. It says to rotate to different areas of the abdomen. It says not to inject into scar tissue, bruises or the navel.
The somatropin label for GENOTROPIN lists the thigh, buttocks or abdomen [3]. It says to rotate the site daily to help prevent lipoatrophy, a loss of fat under the skin.
The bremelanotide label for VYLEESI names the abdomen or thigh, given with an autoinjector [4]. Its instructions say to choose a different site each time and to stay 2 inches from the navel.
Why rotation shows up on every label
Repeated injections in one spot can irritate the skin. The EGRIFTA SV label counts it. In the first 26 weeks of trials, injection-site reactions occurred in 25% of treated patients against 14% on placebo [2]. These included redness, itching, pain, irritation and bruising. The label says rotating sites reduces them.
The longer-term risk is a change in the fat under the skin. The best data here come from insulin, another injected peptide. In a study of 430 insulin users, 64.4% had lipohypertrophy[5]. These are fatty lumps at overused sites.
Rotation made the biggest difference. Of patients who rotated correctly, only 5% had the lumps. Of patients with lumps, 98% did not rotate or rotated incorrectly. Reusing needles more than five times also raised the risk.
Lumps matter because drug absorbs unevenly from them. International recommendations for insulin say not to inject into these lesions, and to rotate sites to prevent them [6]. The same guidance names the shortest needles as the first choice: 4 mm on pens and 6 mm on syringes. It says injections into muscle should be avoided.
How to use this
Read the label that came with your product, and follow its sites. Keep a simple rotation, so no spot gets two doses in a row. Check the area before each injection for lumps, bruises or scars, and skip them.
If a lump or a reaction keeps coming back, tell your prescriber. Preparing a powdered peptide before injecting is covered in how to reconstitute peptides, and the diluent in bacteriostatic water for peptides. Weight-loss injections sit under the weight goal.