How a GLP-1 Weight Loss Injection Works — Step by Step

Step 1: Before you inject, storage, timing and what you will need

Your pen arrives refrigerated and should go straight into the fridge when it lands. Both Mounjaro's KwikPen and the Wegovy pen can tolerate a limited period at room temperature if you need to travel, but the exact window differs between products, follow the Patient Information Leaflet for your specific medicine rather than any general figure you have read online.

Choose a consistent day of the week and stick to it. If your order arrives on a Tuesday after a bank holiday because you placed it just before Christmas, that Tuesday simply becomes your injection day going forward. Consistency matters more than the specific day you pick.

Gather what you need: the pen, a clean alcohol swab to prepare the skin, and a sharps container for the used pen or needle. Never dispose of used pens in household bins, sharps containers are the safe, legal route.

Wash your hands thoroughly before you start. That is not a formality; subcutaneous injections bypass your skin's usual barrier, so cleanliness matters in a way it does not for most medicines you take by mouth.

Step 2: The injection itself (site, technique and what a GLP-1 injection actually feels like

Pinch a fold of skin at your chosen site) abdomen, outer thigh or upper arm all work. Insert the needle at a 90-degree angle (most pre-filled GLP-1 pens guide you automatically) and press the button or plunger until the dose has been delivered. Hold for the count your leaflet specifies, then withdraw. A small amount of redness or a faint sting immediately after is normal.

Rotate your site every week. If you always inject in the same spot, the tissue can thicken and absorption becomes less predictable. Many people find it useful to keep a simple mental map, left side of the abdomen this week, right thigh next week, and so on.

Mounjaro uses a KwikPen that holds four weekly doses; Wegovy comes as individual pre-filled pens. The mechanics differ slightly, so read the specific instructions for whichever product you are prescribed. If a step is unclear, our FAQs page covers common injection questions, and our clinical team is available seven days a week.

For a broader look at what distinguishes the available options, including details on the three weight loss injections most commonly prescribed, the weight loss injections overview sets out the key differences side by side.

Step 3: Managing dose increases and early side effects

Tirzepatide starts at 2.5 mg, a dose whose job is to let your body acclimatise, not yet to drive significant weight loss. Semaglutide starts at 0.25 mg for the same reason. Your prescriber sets the pace of increases; do not try to speed that up, and do not stay at a low dose indefinitely without clinical review.

The GI effects people notice most (nausea, looser stools, a drop in appetite that can feel almost startling) are most pronounced in the first days after starting and after each dose step. For most people they fade within one to two weeks at the new level. Eating slowly, choosing smaller portions of lower-fat food, and keeping well hydrated all help; the NHS patient information for tirzepatide has a full list of what to watch for and when to seek urgent help.

Seek medical help promptly if you develop severe stomach pain that spreads to your back, with or without vomiting, this can, rarely, indicate pancreatitis. The MHRA highlighted acute pancreatitis as a known risk for GLP-1 medicines in a Drug Safety Update in January 2026; report any suspected side effects at the Yellow Card scheme.

Questions about whether the cost of private treatment makes sense for your situation? The cost context for weight loss injections explains what legitimate pricing actually covers.

Step 4: Clinical review, repeat prescriptions and what happens longer term

No injection works in isolation. GLP-1 medicines are licensed alongside a reduced-calorie diet and increased physical activity, that framing is not a disclaimer, it is genuinely how the medicines perform best in practice. Appetite reduction makes the dietary side considerably easier for most people, but the habit-building still needs to happen.

Every repeat prescription at nume involves a fresh clinical review. A real prescriber reads your update (your weight, how you have been tolerating the current dose, any new symptoms) before anything is dispensed. This is not a formality; it is how dose adjustments get made safely and how problems get caught early. Our clinical team is the backbone of that process.

If you reach the highest dose your prescriber has set and weight loss plateaus or falls below five percent over six months, NICE guidance suggests that continuing treatment should be reviewed. That conversation happens with your prescriber, not unilaterally. Treatment is not open-ended by default.

When you are ready to explore whether a weight loss injection is right for you, or you want to understand more about how Mounjaro works as an injection for weight loss, the free consultation is the right starting point. A prescriber reviews your answers the same day, no algorithm, no automated decision.