Using a semaglutide pre-filled pen: a step-by-step guide

Step 1, Preparing the pen before you inject

Take the pen out of the fridge ahead of time and let it reach room temperature; a cold pen can make the injection more uncomfortable. Check the label matches your prescribed dose and look through the viewing window, the liquid should be clear or faintly yellow and free of particles. If it looks cloudy, discoloured or contains visible matter, do not use it and contact your prescriber or our team.

Wash your hands thoroughly. Attach a new needle by removing the paper tab, pushing the capped needle straight onto the pen tip, and twisting clockwise until it is snug. Remove the outer cap and keep it, you will need it for safe disposal. Remove the inner cap and set it aside. You can find guidance on correct needle attachment, along with a full overview of the device itself, on our semaglutide pen page, and further injection technique detail on our how to inject semaglutide page.

If this is a new pen, check whether a flow check (prime) is needed, the Patient Information Leaflet that came with your pen will tell you. Follow those instructions precisely; they are specific to your pen format.

Step 2 (Choosing and preparing your injection site

Semaglutide is injected subcutaneously) into the fatty tissue just beneath the skin, not into muscle. The three licensed sites are the abdomen (at least 5 cm from the navel), the outer thigh, or the outer upper arm. Rotating between sites matters: injecting repeatedly into the same spot can cause lipohypertrophy, a build-up of fatty tissue that slows absorption.

Clean the chosen area with an alcohol swab and let it dry fully before injecting, wet skin can sting and occasionally affects absorption. Pinch a fold of skin if your tissue is slim, or inject flat if there is adequate subcutaneous depth; your prescriber can advise on technique for your body type.

Keep a simple rotation log (a small note on your phone works well) so you are not re-using the same site more often than every four weeks. That consistency makes a quiet but measurable difference to how evenly the medicine is absorbed across the week. Our Wegovy pre-filled pen overview has more on what to expect from the pen itself.

Step 3, Injecting and disposing of the pen safely

Press the pen firmly against the cleaned skin. Press the injection button and hold it down; you will hear a click when the injection starts. Keep the pen pressed against the skin and continue holding the button until you hear or see a second confirmation, this varies slightly by pen design, so check the leaflet for your specific pen. A slow, steady hold (around ten seconds is typical) ensures the full dose is delivered before you remove the pen.

Once you withdraw the pen, the needle retracts automatically. Do not recap the needle with the inner cap. Use the outer cap to lock the needle before dropping it directly into a sharps container, standard household bins are not safe for used needles, and many GP surgeries and pharmacies accept sealed sharps containers for disposal. The used pen body (without the needle) can go into general waste.

A mild pinprick or tiny bruise at the site is normal. Do not rub the area afterwards, as this can affect absorption. If you notice persistent redness, swelling or pain at the site, mention it to your prescriber at your next review. For a detailed walkthrough of the insertion steps, see how to insert the Wegovy pen.

Side effects to know about and when to act quickly

The most common side effects are gastrointestinal: nausea, loose stools, constipation, reflux and reduced appetite are all reported in clinical studies, and they tend to be most noticeable in the first week or two after starting or increasing a dose. Eating smaller portions, avoiding very fatty or spicy food, and staying hydrated helps most people through the adjustment period.

A small number of people experience more serious effects that need prompt attention. Severe stomach pain that radiates to the back (with or without vomiting) can be a sign of pancreatitis. The MHRA issued a Drug Safety Update in January 2026 reminding prescribers and patients that acute pancreatitis is a known though infrequent risk with GLP-1 medicines; if you experience this symptom, stop the injection and seek urgent medical help. Signs of an allergic reaction (swelling of the face or throat, difficulty breathing, a rapid rash) also require immediate emergency care.

You can report any suspected side effect through the MHRA's Yellow Card scheme, linked above. Keeping a note of when symptoms started and whether they coincided with a dose change is useful information for both your prescriber and any Yellow Card report. The semaglutide dose and timing schedule for your specific situation is something to discuss with your prescriber, the semaglutide injection page covers the broader clinical context. For pricing context if you are weighing up options, our Wegovy prices page explains what private treatment typically includes.