How to give a weight loss injection safely and correctly

What do you need before you inject?

Before you pick up the pen, a few simple preparations make the whole process easier and safer. Take your pen out of the fridge around 30 minutes before you plan to inject, a cold pen can sting more, and letting it reach room temperature makes the medicine more comfortable to deliver. Check the liquid through the pen window: it should be clear or very slightly yellow and free from particles. If it looks cloudy or discoloured, do not use it.

Wash your hands thoroughly with soap and water. Choose your injection site (abdomen (at least two inches away from the navel), front of thigh, or outer upper arm) and keep a mental note of where you injected last week so you can rotate. Clean the area with an alcohol swab and allow it to dry fully; injecting through damp skin can cause minor irritation. That brief drying pause is worth it.

The NHS patient information for tirzepatide covers each of these steps in detail, and your printed leaflet mirrors that guidance exactly, keep it to hand for your first few injections.

How do you actually give the injection?

Both Mounjaro's KwikPen and Wegovy's pre-filled pen are designed so that the mechanics are largely automatic once you have the pen in position. There is no needle to attach to the Mounjaro KwikPen; Wegovy requires clicking on a new needle before each use. If you are using Wegovy, our spare needles are available if you need them.

Hold the pen at a right angle (90 degrees) to the skin. For people with very little body fat at the chosen site, a slight pinch of skin can help; for most people, pressing the pen firmly and flat against the skin is sufficient. Press and hold the injection button as directed by your specific pen's instructions. You will hear or feel a click when the dose starts, and another when it is complete. Keep the pen pressed in place for the count of ten before removing it, this helps ensure the full dose is delivered. Do not rub the site afterwards.

For a detailed visual walkthrough of the steps involved in giving weight loss injections, our injection technique guide goes through each stage with practical tips from people who have been doing this for months.

What should you do if something goes wrong?

A small drop of liquid at the injection site after you remove the pen is common and does not usually mean you have lost the dose, most will have been delivered. Apply gentle pressure with a clean tissue if there is any minor bleeding; this is normal and typically stops within seconds.

If you miss your weekly dose and remember within four days, you can give it then and return to your usual day the following week. If the five-day mark has passed, skip that dose and wait for your next scheduled one. Never give two doses to make up for a missed one. Any uncertainty about timing or what to do if you have been unwell should go to your prescriber first and your Patient Information Leaflet second, not online forums.

For broader questions about how these medicines fit into a longer treatment plan, the practical guide to using weight loss injections covers common adjustments and what to expect week by week. And if you are wondering whether your GP will give you weight loss injections, we explain what typically happens when patients raise this with their surgery and what factors influence that conversation.

When should you get medical help?

Most injection-related side effects are mild: a small bruise, brief stinging, or minor redness that settles within a day. These are not reasons to stop. Seek urgent medical attention for any of the following: severe or persistent stomach pain that radiates to the back (which can indicate pancreatitis, highlighted in a January 2026 MHRA Drug Safety Update for GLP-1 medicines, report any suspected side effects via the Yellow Card scheme); signs of a serious allergic reaction such as swelling of the face, lips or throat or difficulty breathing; or severe vomiting that prevents you from keeping fluids down. These are infrequent, but they matter.

If you ever notice changes at the injection site beyond ordinary minor bruising (persistent lumps, hardening of tissue, or signs of infection such as warmth, spreading redness or pus) contact your prescriber. Rotating sites and not reusing needles are the practical steps that prevent most of these problems. The overview of weight loss injections has more on what the clinical trial programmes reported about tolerability.

If you are not yet on treatment and would like a prescriber to assess whether one of these medicines is right for you, our page on whether a GP can give you weight loss injections sets out the current NHS position clearly before you decide how to proceed. If you are also curious about whether a GP can prescribe weight loss injections, we walk through how that process typically works and what your options are. Speak to our prescribers through the free consultation, it takes a few minutes, and a real clinician reads every response the same day.