How to inject semaglutide or tirzepatide: technique, sites, and storage

Semaglutide and tirzepatide are both injected subcutaneously — into the fat layer just under the skin, not into muscle. The mechanics are simple once you've done it a few times, but technique genuinely affects both comfort and, over months of weekly injections, your skin. Here's what matters.

Approved injection sites

The FDA labels for these drugs specify the abdomen, thigh, or upper arm as approved injection sites²³. All three work; which one you use is mostly personal preference and reach (the upper arm is harder to self-inject and often needs a second person, or a pen designed for one-handed use). What matters more than which site you pick is that you rotate within and between them.

Why site rotation isn't optional

Injecting in the exact same small spot week after week is the leading cause of lipohypertrophy — a lumpy, thickened area of fat tissue under the skin from repeated injections in one place. Beyond being uncomfortable, injecting into lipohypertrophic tissue can also affect how consistently the medication absorbs, which matters for a drug where consistent weekly dosing is the whole point. The foundational clinical consensus on injection technique — developed originally for insulin but broadly applicable to any subcutaneous weekly injectable — recommends systematically rotating sites (for example, working across quadrants of the abdomen from week to week) specifically to prevent this¹. A simple system — moving a set distance from last week's spot, or mentally dividing your abdomen into quadrants and rotating through them in order — is more reliable than 'somewhere different' as a mental note.

Needle and technique basics

Most GLP-1 pens come with a needle already sized appropriately for subcutaneous injection and don't require you to select a length — a meaningful simplification compared with older insulin regimens where needle length was a bigger individual decision¹. Pinching a fold of skin before injecting (if your specific pen's instructions call for it), inserting at the angle specified in your product's instructions for use, and injecting steadily rather than rushing all reduce discomfort and bruising. Always follow the specific instructions for use that ship with your prescribed pen — pen mechanisms differ slightly between manufacturers and even between products from the same manufacturer, and generic 'how to inject' advice can miss a device-specific step.

Storage — follow your pen's printed instructions

Before first use, GLP-1 pens generally need refrigeration; after first use, many can be kept at room temperature for a limited window, but that window and the exact refrigeration requirements differ by product and have changed as manufacturers have introduced new pen designs. Don't rely on a generic rule of thumb here — check the instructions for use and the printed expiration information that ships with your specific pen, and never use a pen that's been frozen, left in direct heat, or used past its labeled expiration.

What good technique doesn't fix

Site rotation and proper technique reduce local injection-site reactions — redness, itching, mild swelling — but they don't change the systemic side effects of the drug itself, like nausea, which come from the medication working as intended rather than from injection technique. See GLP-1 side effects: what to expect for that fuller picture, and semaglutide dosing and titration or tirzepatide dosing and titration for how the dose schedule itself is staged. This is general technique information — always defer to the specific instructions for use that ship with your prescribed medication, and ask your pharmacist or prescriber to walk through your first injection if anything is unclear.