Mounjaro pen colours: what each colour tells you about your dose

Step 1: identify your pen before you open the box

When your Mounjaro arrives (tracked by DPD, in a plain unbranded box you'd never look twice at) the first thing worth doing is checking the pen colour against your prescription. Eli Lilly uses a consistent colour code across every component of the KwikPen: the label, the coloured cap, and the markings on the device itself all carry the same shade. The six colours are:

Grey (2.5 mg), the starting strength. Its only job is giving your body time to adjust before you move to a therapeutic dose.

Red (5 mg), the first full dose step, typically reached after four weeks at 2.5 mg if your prescriber agrees.

Yellow (7.5 mg), the midpoint of the schedule for many people.

Blue (10 mg), a step many patients settle on long-term.

Teal (12.5 mg), the penultimate strength.

Purple (15 mg), the highest licensed dose; SURMOUNT-1 trial data showed average body-weight reductions of around 20–21% at this level over 72 weeks, as cited in the New England Journal of Medicine.

Checking the colour is a 3-second habit that rules out the most common injection error: using last month's pen instead of your current one after a dose increase.

Step 2: match the colour to your current prescription before every injection

Dose increases in the Mounjaro schedule are clinical decisions. If your prescriber moves you from, say, yellow to blue, you'll receive a blue-labelled pen for the next four weeks. The colour change is the most immediate visual cue that something is different. Keep old pens stored separately once you've started a new strength, or dispose of them promptly in a dedicated sharps container, mixing them up is easier than it sounds, especially if you store them in a fridge door alongside other household items.

The NHS medicines page for tirzepatide notes that each pen should be stored refrigerated between 2–8°C; the exact window for room-temperature use is detailed in your Patient Information Leaflet, and that's the right place to check it rather than any third-party source. If you've ever wondered whether a cold pen straight from the fridge is fine to inject, that's a question our page on injecting Mounjaro cold covers in full.

Understanding the KwikPen device itself helps too, particularly how the dose window confirms delivery once the injection is complete.

Step 3: use the colour check as part of a consistent injection routine

A repeatable injection routine reduces errors and injection-site discomfort. The colour check fits neatly at the beginning: confirm the pen colour, inspect the liquid through the viewing window (it should be clear and colourless to slightly yellow), check the expiry date on the label, and then proceed with site selection. Mounjaro can be injected into the abdomen, thigh, or upper arm, rotating the site each week is recommended in the SmPC to reduce local skin reactions.

Full step-by-step technique, including how to attach the needle, set the dose window, and confirm injection is complete, is covered in detail on the how to use the Mounjaro pen page. For needle changes specifically, compatible replacement needles are available if you need to stock up between prescriptions. The Mounjaro injection overview is also a useful reference for anyone starting treatment for the first time.

One point that catches people out: the colour of the liquid inside the pen is not the same as the pen's colour-coded label. The liquid itself is always pale and clear. The safety colour-coding is on the outside of the device only.

Why the colour system matters for your prescriber too

When you report back to our clinical team or your GP, being specific about which pen you're on is straightforward if you know the colour: "I'm on the blue pen" is quicker and less prone to error than recalling a number under pressure. If you're ever transferring to a new provider or discussing your treatment with a GP, the colour is an instant reference point any UK clinician will recognise.

It's also relevant to cost. The six strengths are priced differently across private providers, and understanding which pen you're at helps you read a prescription or an invoice accurately. Our Mounjaro cost guide explains how private pricing is structured across the dose range, including what the Eli Lilly list price increases in 2025 mean for patients. For a broader view of the Mounjaro treatment programme, the main Mounjaro page covers the full picture, eligibility, mechanism, and how the prescription process works through a regulated service.

Mounjaro is a prescription-only medicine. The dose you use, and when you increase it, is a decision made with a prescriber who has reviewed your health, not a choice based on the colour alone. If you're not yet on treatment and want to see whether you'd be eligible, you can check your eligibility with our prescribers at no cost.