Mounjaro Needle Tips: Which Pen Needles to Use (October 2026)

01 · The core answer

Which needle should you use with Mounjaro?

Use the pen needle that arrives with your order, or another needle that the Mounjaro patient leaflet says is compatible with the KwikPen.¹³ Mounjaro is a pre-filled multi-dose pen, so the medicine is already inside. Only the needle is separate.¹

Needle length and thickness are covered in more depth in our guides on how many mm the Mounjaro needle is and the UK needle size guide.

In general, a pen needle that is short and fine causes less discomfort than a long, thick one. Short needles are designed to deliver the medicine into the fatty layer just under the skin, which is where this injection goes. If you are unsure, ask the prescribing team during your monthly review.

02 · Getting needles

Do you need to buy needles separately?

Not if you order from us: needles, a sharps bin and injection guidance are included with every order. That covers your first pen and every repeat order.

If you need extra needles, for example after a dropped needle or a travel mishap, you can add pen needles to your basket. Our Mounjaro pen starts at £169.99 per month at the 2.5mg dose, and the consultation is free.

Be careful with unbranded needle listings from marketplaces or social media sellers. A needle is a sterile medical device, so buy from a registered pharmacy such as ours (GPhC 9012878) or another regulated supplier.

03 · What to do next

Where to go from here

If you are about to start, read the injection guidance in your box and the leaflet before your first dose. Our Mounjaro tips page covers the wider routine, and top tips collects what experienced users find most useful. If you are not yet a patient, our weight loss clinic explains how the free consultation works.

04 · Preparing the pen

Preparing the pen and needle

Always read the patient information leaflet that comes with your pen, because it holds the step-by-step instructions.¹³

Before you start, wash your hands and check the pen label. Make sure it is the strength your prescriber confirmed. The pen is a fixed strength, so a 2.5mg pen stays a 2.5mg pen throughout.¹ Look at the medicine through the window. If it looks discoloured, cloudy or has particles, do not use it.

Take a new needle from its sealed pack and check that the seal is intact. Do not use a needle from a pack that looks damaged, wet or already opened. Attach it as the leaflet shows, and remove both caps only when you are ready to inject.

• Check the pen strength and the label every time.
• Use a new needle from an unopened sealed pack.
• Keep the needle covered until the moment you inject.
• Never share a pen or a needle with anyone, even another family member.

05 · Injecting comfortably

How to inject more comfortably

The most useful comfort tip is to rotate your injection site each week and follow the leaflet's technique.¹³ Licensed injection sites are the stomach area (at least 5cm from the belly button), the front of the thigh, or the back of the upper arm if someone else gives the injection. Moving to a fresh patch of skin each week helps avoid soreness and lumps building up in one spot.

Choose clean, dry skin that is not bruised, scarred or tender. Let the skin relax before injecting. Tense muscle makes any needle feel sharper. If you use alcohol to clean the skin, let it dry fully first, as wet alcohol can sting.

People often ask whether to pinch the stomach. The leaflet and the instructions in your box set out the exact technique for the pen. Follow those rather than a forum tip, since the right approach can depend on how much fatty tissue you have at the site. If you are unsure, ask your prescriber or pharmacist to talk you through it.

Inject with the pen held steady and straight, and follow the pen's instructions on how long to keep it in place. Pulling away early is a common cause of leaks and wet patches. A small drop of fluid or a tiny spot of blood can happen occasionally and is usually not a concern, but tell your prescriber if it keeps happening.

06 · Clicks and dosing

Clicks, doses and what one pen holds

Each KwikPen is made as one fixed strength, and you take the dose that matches the pen your prescriber supplied.¹ The pen is designed to deliver that strength when you follow the leaflet.

That is why questions such as "how many clicks gets me 5mg from a 7.5mg pen" have no safe do-it-yourself answer. If you think your dose should change, speak to your prescriber, who can move you to the right strength.

As for how long a pen lasts, one pen is a month's supply of weekly doses, which is how we price it. Once in use, a pen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away. Do not use a pen that has been above 30°C or has been frozen.¹³ Unopened pens belong in the fridge at 2–8°C until first use.

Dose steps are planned by your prescriber. Our guide to starting needle needs covers what to have ready on day one.

07 · Reuse and disposal

Reusing needles and disposing of them safely

Use a fresh needle for each injection and do not reuse it.¹³ A used needle is no longer sterile, and it can blunt or bend, which makes the next injection more painful. Our explainer on reusing a Mounjaro needle goes through the reasons in more detail.

After injecting, remove the needle as the leaflet shows and place it straight into a sharps bin. Never put loose needles in household rubbish or a recycling bin. When the sharps bin is nearly full, ask your pharmacy or local council how to hand it in. Arrangements differ by area.

If you prick yourself with a used needle, wash the area with soap and water and seek advice from a pharmacist or your GP. We have a separate page on what to do if you accidentally prick a finger with a Mounjaro needle.

08 · Needle depth and problems

Needle depth, bleeding and other problems

The needle is meant to go through the skin into the fatty layer beneath, not into muscle. You can read more about how deep the needle goes and how far it goes in. If you have very little fatty tissue, or injections regularly feel deep, tell your prescriber so they can advise.

Common needle-related problems are easy to fix:

• Pain on injecting: check you are using a fresh needle, relax the area, and rotate sites.
• Leaking from the site: check you kept the pen in place for the time the instructions state.
• Bruising: avoid areas that already look bruised, and try a different site next week.
• A blocked or bent needle: remove it safely and use a new one. Do not force the pen.

Contact your clinical team if a reaction is spreading, hot, very painful, or lasts more than a week. For side effects of the medicine itself, the leaflet lists them, and you can report any suspected side effect through the Yellow Card scheme.¹⁹

09 · Other pens and needles

Mounjaro needles versus Wegovy and other pens

Do not assume that needles for one injectable work with another. Mounjaro and Wegovy are different products with different pens, and each has its own leaflet.¹¹⁸ For semaglutide pens, check the Wegovy leaflet or ask your prescriber, rather than borrowing advice written for Mounjaro.

If you ever switch treatments, ask for the needle and storage instructions for the new product.

Mounjaro is licensed for weight management and type 2 diabetes in adults, and is taken once a week alongside a reduced-calorie diet and increased physical activity.¹ Needle technique matters because you only inject once a week, so getting the routine right makes every dose easier. Individual results vary.

10 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹