Subcutaneous Injection

Quick definition. A subcutaneous injection delivers medication into the layer of fat just beneath the skin, not into a muscle or vein. Nearly all injectable GLP-1 medications are given this way using a pre-filled pen.

What "Subcutaneous" Means

Subcutaneous (often abbreviated "subcut" or "SC") refers to the tissue layer directly under the skin and above the muscle — the same fatty layer you can pinch between two fingers. A subcutaneous injection uses a short, fine needle to deposit medication into this layer. It sits between an intramuscular injection, which goes deeper into muscle, and an intradermal injection, which goes shallower into the skin itself.

Why GLP-1 Medications Use This Route

The subcutaneous layer has a relatively modest blood supply, so a drug placed there is absorbed slowly and steadily rather than all at once. For long-acting GLP-1 receptor agonists, this gradual absorption is a feature: it helps maintain stable drug levels across a full week between weekly doses and smooths out the peaks that would otherwise worsen nausea. The route is also practical — subcutaneous tissue can comfortably hold the small liquid volumes these drugs require, and the technique is simple enough for patients to self-administer at home.

Common Injection Sites

The FDA labels for Ozempic, Wegovy, Mounjaro, and Zepbound all specify three approved sites: the abdomen (avoiding a two-inch radius around the navel), the front of the thigh, and the back of the upper arm. Patients are advised to rotate sites with each dose to reduce the chance of skin irritation or fatty lumps (lipohypertrophy) that can develop when the same spot is used repeatedly. The injection can be given regardless of meals.

The Pen Devices

Most GLP-1 medications come as pre-filled, disposable pen injectors with a hidden or very fine needle, designed so patients never have to draw the drug from a vial. Some pens deliver a fixed dose per click; others must be dialed to the correct dose during titration. Zepbound is also available in a single-dose vial. The pen format is a major reason these once-weekly therapies became practical for routine self-care.

Which GLP-1s Are Not Injected

Not every GLP-1 medication is subcutaneous. Two are taken by mouth: Rybelsus, an oral tablet form of semaglutide, and Foundayo (orforglipron), a non-peptide oral agent. Oral formulations remove the needle entirely but come with their own rules — Rybelsus, for instance, must be taken on an empty stomach with a small sip of water and a 30-minute wait before eating or drinking anything else, because food sharply reduces its absorption. For patients weighing injectable versus oral options, this trade-off between dosing convenience and absorption requirements is often the deciding factor.