How to give yourself a Mounjaro injection, step by step

The moment your pen arrives

Picture the scene: the DPD parcel is on the doorstep, you open the box, and inside is a slim white pen you have never used before. Most people's instinct is to look for a syringe, there isn't one. The Mounjaro KwikPen hides the needle inside a capped tip, so you never see it enter the skin. Before anything else, check the expiry date printed on the label and look at the liquid through the pen window. It should be clear or very slightly yellow and free of particles. If it looks cloudy, discoloured, or has floating bits, do not use that dose and contact your prescriber.

Wash your hands thoroughly, then decide where you're injecting today. The licensed sites for Mounjaro are the belly (at least five centimetres from the navel), the front of the thigh, and the outer upper arm. Rotating around these sites from one injection to the next keeps the skin healthy and helps absorption stay consistent. Understanding which sites tend to work best for different people is worth reading before you settle on a routine.

Clean the chosen spot with an alcohol swab and let it dry fully, wet skin can sting. Drying takes about fifteen seconds, but most people rush this step. Take the moment.

Pressing, clicking, and counting to ten

Pull the grey base cap straight off. Do not twist it, the mechanism is not designed for that and you risk damaging the seal. Attach a fresh needle by peeling the paper tab from the inner needle cap, placing it onto the pen tip, and turning clockwise until it sits snugly. Then pull off the outer needle cap and the inner needle cap, setting them aside, you'll need the outer cap later for safe disposal.

Hold the pen so the window faces you (so you can watch the dose counter move). Press the pen firmly against the cleaned skin at a ninety-degree angle. Press the injection button once with your thumb, you will hear a click. Keep the pen pressed against your skin and count steadily to ten. A second click usually happens around the five-second mark; that confirms the dose is releasing. Do not lift the pen early. When you remove it after ten, the dose counter will have moved down by one number, confirming the dose was delivered.

If you would like a thorough walkthrough before your first dose, our page on how to give the Mounjaro injection covers what to do if the counter does not move and when to contact your pharmacy or prescriber. That step is important, do not simply re-inject if you are unsure whether the dose went in.

After the dose: sharps, storage, and side effects to watch for

Recap the needle using only the outer cap you set aside (never use your fingers to re-cover a needle tip). Unscrew the needle and place it directly into a proper sharps container, household bins are not safe for used needles, and your local council or pharmacy can advise on collection. Replace the grey base cap on the pen and return it to the fridge.

Some redness or a small raised patch at the injection site is normal and usually settles within a day. A question our prescribers hear most weeks is whether a slight lump under the skin means something has gone wrong, it almost always just means the tissue is adjusting, particularly in the first few injections at a new site. Rotating properly tends to resolve it.

Mild nausea is the most common side effect in the early weeks of Mounjaro treatment, particularly in the days after an injection. It tends to ease as the body settles at a given dose. Eating smaller portions and staying well hydrated helps many people. The NHS tirzepatide patient page lists the full side-effect profile and explains which symptoms mean you should seek medical help promptly, including severe stomach pain that spreads to the back, which should always be assessed urgently.

The practical habits that make weekly injections easier

Set a weekly reminder on your phone for the same day each week, Monday mornings, say. Consistency in timing keeps your routine anchored and makes missed doses less likely. If you do miss a dose, refer to your Patient Information Leaflet and contact your prescriber rather than doubling up the following week. Missed doses and timing adjustments are covered in detail in the SmPC, accessible via the electronic Medicines Compendium.

A few things that make the weekly process smoother in practice: take the pen out of the fridge ten to fifteen minutes before injecting, since a room-temperature injection tends to be more comfortable than a cold one. If you are new to self-administering this medicine, our guidance on how to inject yourself with tirzepatide is a reassuring read before you start. Keep a spare box of compatible injection needles so you are never caught short on a Sunday evening. And if you ever feel uncertain about anything (the appearance of the liquid, an unusual skin reaction, a counter that did not behave as expected) the right call is always to pause and contact your prescriber rather than push ahead and hope.

Mounjaro is a once-weekly subcutaneous injection and each KwikPen holds four doses, so you will typically open one new pen each month. For a fuller picture of how the medicine works and what the clinical evidence says, the Mounjaro overview page is a good starting point. If you are exploring weight-loss treatment options more broadly, our treatment page sets out everything available through nume. And if cost is part of your thinking, an honest look at what Mounjaro actually costs in the UK puts the numbers in context.

When you are ready to speak with a prescriber, start a free consultation and our team will review your situation the same day.