Every subcutaneous injectable label STACK has read says the same thing: rotate. This page explains why, which body areas the labels name, and how the site picker in STACK works. It is not instruction on how to inject; your prescriber or pharmacist shows you that, and the product’s Instructions for Use governs.

What the labels say

The Mounjaro and Zepbound labels instruct: “Inject subcutaneously in the abdomen, thigh, or upper arm” and “Rotate injection sites with each dose” [1][2]. The Ozempic label uses the same three areas and tells prescribers to “instruct patients to use a different injection site each week when injecting in the same body region” [3]. The patient Medication Guides put it as: “Change (rotate) your injection site with each weekly injection. Do not use the same site for each injection” [1][3].

The Zepbound Instructions for Use are the most specific about which sites are practical alone: “You or another person may inject into your stomach (abdomen) or thigh. Another person can inject into the back of your upper arm” [2]. It also says you may keep using the same body area as long as you pick a different spot within it [2]. Insulin labels add a fourth region: Humulin R lists “the thigh, upper arm, abdomen, or buttocks” [4]. And a peptide label that restricts injection to the abdomen still says to rotate within it and to avoid “scar tissue, bruises or the navel” [5].

Why rotate: lipohypertrophy

Lipohypertrophy is “the development of lumps, raised areas, firmness, or hardness in the fatty tissue under the skin caused by the repeated injection or infusion of insulin” [7]. It develops “primarily due to repeated injections at the same place — generally over months to years,” and the risk factors include not rotating within or between sites and reusing needles [6]. It is common: 48.7% of long-term insulin users in one Italian study [8], 57.0% of type 1 and 55.5% of type 2 patients in a Jordanian clinic sample [7], and roughly 30–50% or more across published surveys [6].

It matters because it changes absorption. In a crossover trial using a euglycemic clamp, injections into lipohypertrophic tissue showed “blunted insulin absorption and significantly increased pharmacokinetic variability compared with injections into normal tissue” [6]. Patients with these lesions used more insulin daily yet had worse glucose control [6]. The Zepbound Instructions for Use tie rotation directly to this: rotate “to reduce your risk of getting lipodystrophy (pits in skin or thickened skin) and localized cutaneous amyloidosis (skin with lumps)” [2]. Humulin R’s label gives the same reason [4]. The same instruction follows: “Do not inject where the skin has pits, is thickened, or has lumps. Do not inject where the skin is tender, bruised, scaly or hard, or into scars or damaged skin” [2].

Why rotate: absorption consistency

Rotation is not about getting more drug in; it is about getting the same amount in each time. The tirzepatide and semaglutide labels report that similar exposure was achieved from the abdomen, thigh, or upper arm [1][2][3], so switching among the three labeled areas does not change the estimated level in STACK. Injecting repeatedly into damaged tissue, by contrast, makes absorption lower and less predictable [6]. In diabetes studies, rotating sites and the absence of lipohypertrophy were each independently associated with better glycemic control [7], and a program that taught rotation and moved patients off damaged sites was followed by measurable improvements over three months [8].

The rotation idea

The principle is simple: spread injections out in space and in time so that no patch of tissue is hit repeatedly. In the randomized trial that taught proper technique, patients were shown to space injections within a site at least 1 cm apart, to avoid reinjecting at a previous spot for 2 to 4 weeks, and to use each of the four main locations rather than only the abdomen [6]. Those figures describe what that trial taught; your own product’s Instructions for Use and your prescriber’s guidance are what apply to you. A written or app-based record makes the pattern visible, which is the part most people find hardest to keep in their head.

How STACK tracks sites

Each logged dose has a site field. STACK’s default site list is:

Abdomen: left upper, left lower, right upper, right lower
Thigh: left, right
Upper arm: left, right
Glute: left, right

The abdomen is split into four quadrants because it is the most-used area [8] and the one where clustering happens most easily. The upper-arm entries are there because labels list the back of the upper arm as a site, usually one that another person injects for you [2]. The glute entries exist because some insulin labels list the buttocks [4]; STACK leaves them switched off unless you turn them on, and you should only do that if a clinician has told you to use that area.

The dose log keeps the site with each entry, so you can look back and see which spots were used recently and which have not been used for a while. STACK does not pick the site for you. If a site looks or feels different — a lump, firmness, a pit, persistent bruising — the labels say not to inject there [2], and that is a reason to call your prescriber.

Free tools

Sources

Every URL below was fetched and checked on 2026-09-24. Bracketed numbers in the text link here.

Injection site rotation: why labels say to rotate, and how STACK tracks sites