Weight Loss Pens UK explains weight-loss injection pens as devices as well as medicines: how the Mounjaro and Wegovy pens work, how to use and store them, and which side effects the UK labels list.

Start here

  • Weight loss pens, explained: what the pens are, what the trials show and how to avoid illegal online sellers.
  • The Mounjaro pen: the KwikPen format, its strengths, the weekly routine and storage.
  • The Wegovy pen: the pre-filled weekly injection, its dose ladder and storage.
  • Using and storing a pen: injection sites, needles, fridge storage, travel and disposal.
  • Side effects: Wegovy frequencies from the UK label, Mounjaro frequencies from the SURMOUNT-1 trial, and the serious risks.
  • The FAQ and the guides to single topics.

Why focus on the pen?

Many everyday questions are about the device rather than the drug: which needle to use, where to inject, how long a pen can stay out of the fridge, how to travel with it and how to dispose of it safely. The Mounjaro and Wegovy pens also differ in how they are set up, primed and stored, so the guides treat them separately where it matters.

Reference points

Device and storage details come from each pen's UK Summary of Product Characteristics, patient information leaflet and instructions for use, published on the electronic Medicines Compendium. Side-effect figures come from the same UK labels and, for Mounjaro, the SURMOUNT-1 trial, safety warnings from the MHRA, and practical health advice from the NHS. Every page shows when it was published, reviewed or last updated.

What we will never do

We will not sell, supply, prescribe or dispense medicines, or link to anyone who does. Weight Loss Pens UK is written by its editorial team and is independent of the manufacturers, with no affiliation with Eli Lilly and Company, Novo Nordisk or any other. Manufacturer and regulator pages are cited as sources for label information only.

Using this information safely

Weight-loss injection pens are prescription-only medicines. Whether one is suitable for you is a decision for a qualified prescriber after a consultation, not this website, and the leaflet supplied with your own pen comes first. Nothing here is medical advice. Report suspected side effects through the MHRA Yellow Card scheme and speak to your GP or pharmacist.