The semaglutide weekly injection: what actually happens, dose by dose

Your first pen arrives, here is what you are actually holding

Picture this: a plain, unbranded box lands via DPD tracked delivery the next working day. Inside is a pre-filled Wegovy pen, cold-chain packaged, alongside an information leaflet that runs to several pages. The pen itself is small, pre-set to a single dose, and uses a concealed needle that retracts automatically after injection. You do not need to measure anything or draw up a dose. The mechanism is designed so that the injection process takes only a few seconds once you are in position.

The first pen contains the 0.25 mg starting dose. This is not the therapeutic dose in the sense of producing significant weight loss, its job is to let your body adjust to the medicine without a heavy hit of gastrointestinal side effects. Nausea, loose stools and stomach discomfort are common early on; starting low reduces how pronounced they tend to be. The full Wegovy treatment overview covers what the titration schedule looks like across the coming months.

Storage matters: the pen must be kept refrigerated between 2°C and 8°C until you are ready to use it. For exact guidance on how long it can sit at room temperature, check the Patient Information Leaflet that comes with your pen, that leaflet, not a webpage, is the authoritative source for those figures.

Choosing where on your body to inject, and why it matters

Semaglutide is injected subcutaneously, into the fatty tissue just beneath the skin, not into muscle. The three licensed sites are the abdomen (avoiding the two inches around the navel), the front or outer thigh, and the upper arm. Rotating between sites, and within each site, prevents the skin thickening called lipohypertrophy that can reduce how reliably the medicine absorbs.

Most people find the abdomen straightforward to reach and use it most often. The thigh works well if you prefer to sit during the injection. The upper arm is an option, though it is harder to administer to yourself than the other two. Whichever you choose, clean the area first (alcohol swabs are the standard approach) and let the skin dry before injecting. Pinch a small fold of skin, insert at roughly a 45 to 90 degree angle depending on your build, press the button, and hold for a count of five or six to let the full dose deliver.

A question our prescribers hear regularly: what if you miss a dose? The answer depends on timing, and for that you should follow the instructions in the Patient Information Leaflet and check with your prescriber. Never double up doses to compensate. The weekly versus daily dosing question is one that comes up a lot, particularly for people switching from other treatments.

Side effects that are common and the ones that need prompt attention

The side-effect profile of semaglutide injections is well characterised from large-scale trials, covering everything from how nausea tends to peak after a new dose to the rarer effects that need prompt medical attention. Gastrointestinal effects are the most frequently reported: nausea, vomiting, diarrhoea, constipation, reflux, and burping. They are most noticeable in the first days after a new or increased dose, and most people find they settle within a week or two as the body adjusts. Eating smaller portions, avoiding rich or fatty foods around injection day, and staying well hydrated all help.

Fatigue and headache are also reported, particularly early in treatment. Injection-site redness or mild irritation can occur and usually resolves on its own.

Some effects need you to contact a doctor promptly. Severe, persistent stomach pain (particularly pain that radiates through to the back, with or without vomiting) should not be waited out, as it can signal pancreatitis. The MHRA has flagged acute pancreatitis as a known, if infrequent, serious side effect of GLP-1 medicines; their Yellow Card scheme allows patients to report suspected side effects directly. Signs of an allergic reaction, symptoms of gallbladder problems, or severe dehydration from persistent vomiting or diarrhoea also warrant medical attention without delay. If you are ever uncertain, contact your prescriber or call 111.

Who the weekly injection is licensed for, and the private route if the NHS wait is long

The licensed criteria for Wegovy cover adults with a BMI of 30 or above, or 27 to 29.9 alongside at least one weight-related condition such as high blood pressure, raised cholesterol, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply under UK guidance for some ethnic backgrounds. If you want to understand exactly how the Wegovy weekly injection works before committing, that page walks through the practicalities in full. Semaglutide is not licensed for people who are pregnant, breastfeeding, or trying to conceive, and it is not licensed for under-18s.

On the NHS, NICE's appraisal of semaglutide (TA875) restricts access to specialist weight management services with multidisciplinary support, and for a maximum of two years. Waiting lists can stretch considerably. For people who do not meet the NHS thresholds or prefer not to wait, a private prescription through a regulated online pharmacy is the legal alternative, provided there is a genuine clinical assessment first. If you would like to understand how the medicine itself works before you begin, the semaglutide injection page covers the pharmacology and what to expect in plain terms.

At nume, every consultation is read by a GPhC-registered Independent Prescriber on the day it is submitted. There is no algorithm making the call. If you want to understand what the assessment covers before you start, our free consultation page explains each step. For a broader look at all the options available, the weight loss treatments page covers the full picture.