How to take the Mounjaro KwikPen: a step-by-step injection guide

The pen is out of the fridge, what to do before you inject

Picture a Monday morning: you open the fridge, take out your Mounjaro KwikPen, and set it on the counter. Give it roughly 30 minutes to reach room temperature. Injecting a cold solution is uncomfortable and entirely avoidable.

While you wait, wash your hands thoroughly. Then look the pen over. Check the liquid through the viewing window, it should be clear to slightly yellow and free of floating particles. If it looks cloudy, discoloured, or contains visible specks, don't use that dose; contact our support team or your prescriber.

Take a fresh needle from your pack and screw it straight onto the pen cartridge holder until it sits snug. Peel away the outer cap and keep it, you'll need it to remove the needle safely afterwards. Then pull off the inner needle cap and discard it. If this is the first time you're using the pen, you'll need to prime it before that first injection; the priming process takes under a minute and removes air bubbles from the needle.

Wipe your chosen injection site with an alcohol swab and let it dry completely, wet skin can sting. That quick skin-check and wipe routine takes less than 60 seconds and is worth building into the habit from day one.

Selecting your dose and completing the injection

Turn the dose selector dial until your prescribed dose number lines up with the pointer. You'll hear and feel a click for each unit, don't press the injection button while you're dialling. Once the number is confirmed in the window, you're ready.

Pinch a fold of skin at your chosen site, hold the pen at roughly a 90-degree angle, and press it flat against the skin. Press the injection button firmly and hold it down. Keep holding, the full dose takes a few seconds to deliver. The viewing window changes from coloured to clear when the dose is complete. It's a small detail, but watching that window is the easiest way to know the injection is done rather than guessing.

Withdraw the pen and release the skin fold. There's no need to rub the site. If a small drop of liquid appears at the surface, that's normal and not a sign the dose was lost. For more on what to expect at each stage, the injection overview covers the practicalities in detail.

Rotate your injection site each week. The abdomen, outer thigh, and upper arm are all licensed sites, the NHS guidance on tirzepatide confirms these three areas. Returning to exactly the same spot every time can cause fatty lumps to develop under the skin, which slows absorption.

Changing the needle and storing the pen between doses

After each injection, re-cap the needle using the outer cap you set aside. Give the cap a gentle twist to loosen the needle, unscrew it, and drop it directly into a sharps container. Never try to re-sheath a bare needle by hand. Needles are single-use, a blunted needle makes the next injection more uncomfortable and increases the risk of infection.

The pen goes back in the fridge without a needle attached. Storing it needle-on creates a risk of air entering the cartridge and leakage between doses. Leave it in its cardboard sleeve if you like, that protects the viewing window from light.

If you need guidance on which needle gauge to use with your pen, the needle guide has the specifics. And if you want a full walkthrough of operating the device, including a clear explanation of how the dose counter works, our guide to using the Mounjaro KwikPen explains the mechanics clearly.

Side effects to know about, and when to act quickly

The most common effects after starting tirzepatide are gastrointestinal: nausea, loose stools, indigestion, or reduced appetite. These tend to be most noticeable in the first week or two after a new dose, then ease. If you want practical advice on timing your meals and what to expect on injection day, our page on how to take Mounjaro helps most people through the adjustment period.

Some effects do need prompt attention. Severe stomach pain that spreads to your back (especially if it doesn't pass quickly) should be assessed urgently. The MHRA issued a Drug Safety Update in January 2026 specifically flagging acute pancreatitis as a known but infrequent risk with GLP-1 medicines; don't wait to seek help if that symptom pattern fits. Signs of a serious allergic reaction (swelling of the face or throat, difficulty breathing) are also an emergency.

For anything less urgent, our prescribers are available seven days a week through aftercare. Suspected side effects can also be reported directly to the MHRA via the Yellow Card scheme, something worth knowing exists even if you never need it.

Tirzepatide is a prescription-only medicine. If you haven't yet spoken to a prescriber about starting treatment, you can check your eligibility through a free consultation with our clinical team.