What is Mounjaro?
Mounjaro is licensed for the treatment of patients who are overweight or living with obesity. When used alongside a balanced diet and regular physical activity, Mounjaro can help people lose weight by regulating appetite and increasing energy expenditure.
Its active ingredient, tirzepatide, acts as a dual GIP and GLP-1 receptor agonist, mimicking the natural hormones GIP and GLP-1.
What does Mounjaro do?
Mounjaro is prescribed for the long-term management of weight after clinical trials demonstrated its suitability for weight loss.
Tirzepatide activates both GIP and GLP-1 receptors. These incretin hormones play an important role in insulin secretion, satiety, and energy balance. By acting on both receptors, Mounjaro improves blood sugar levels and enhances feelings of fullness.
Its effects last only while you take it. When used correctly alongside a healthy diet and exercise, it can support weight loss. For more information on this, see our blog article here.
What’s the difference between Mounjaro and Wegovy?
Both are effective weight-loss treatments, but they work in slightly different ways:
Wegovy contains semaglutide, which mimics GLP-1. GLP-1 helps control appetite, slow digestion, and improve blood sugar levels.
Mounjaro contains tirzepatide, which mimics both GLP-1 and GIP. GIP also helps regulate blood sugar and appetite.
Wegovy also has proven cardiovascular benefits for people with obesity and existing heart disease. In the SELECT trial, involving more than 17,000 adults, people taking Wegovy 2.4 mg weekly were 20% less likely to experience a serious heart problem. Wegovy is the only weight-loss medication licensed in the UK to reduce this risk.
What doses of Mounjaro are available?
Mounjaro comes in 6 doses:
2.5mg
5mg
7.5mg
10mg
12.5mg
15mg
You'll start on 2.5mg, and your clinician will increase your dose over time. See Will I be on a maintenance dose? for how this works.
What if I see air bubbles in my pen?
A small pocket of air can appear during priming, injection, or following temperature changes. Keep the pen steady and avoid shaking or tapping it.
It is generally safe to inject Mounjaro with a small air bubble. The tiny amount of air will not cause harm or affect the medication’s effectiveness. Mounjaro is injected under the skin, and air bubbles are mainly a concern when injected directly into a blood vessel.
If you accidentally inject a large amount of air, monitor for unusual symptoms and consult your healthcare provider if you experience an adverse reaction.
Why am I missing a dose from my Mounjaro pen? / Why is there no excess medication left?
If you have recently received the updated Mounjaro KwikPen (rolled out starting April 2026), you are not missing a dose. Every pen, regardless of the version, is designed to deliver exactly four doses of your prescribed medication.
Why does it look like a dose is missing?
If you have received the updated Mounjaro KwikPen introduced from April 2026, you are not missing a dose. Every pen is designed to deliver exactly four doses.
New pens contain less excess liquid previously included for priming, so the plunger sits near the end of the window after the fourth dose. Older pens contained roughly 3 mL of total liquid, with each dose measuring approximately 0.6 mL, leaving a small amount after the fourth dose.
Repeated or excessive priming can use up the extra liquid and may leave insufficient medication for all four doses. Follow the priming instructions carefully.
The updated pen also has a clearer completion marker: after your fourth and final dose, the plunger will sit close to the end of the pen window, showing that the pen is ready to be safely discarded.
Both versions are safe and deliver four prescribed doses.
Are there any side effects?
Like all medicines, Mounjaro can cause side effects, although not everyone experiences them. Most patients find they improve over time as the body becomes accustomed to the medication.
If your side effects are not resolving, speak to one of our clinicians. You can also refer to the Mounjaro safety information and the patient information leaflet supplied with the medication.
When can I take Mounjaro?
Mounjaro is injected once a week. There is no specific time of day when it must be administered, provided you use it on the same day each week and around the same time. You can take it with or without food.
You can change your weekly injection day as long as your last dose was taken at least 3 days earlier.
How do I take Mounjaro?
For detailed instructions, refer to the leaflet inside your medication box.
Priming prepares the needle and delivery system for accurate medication flow, helping you receive the full prescribed dose. The small amount of liquid released during priming is not part of your prescribed doses and must not be injected.
Step 1: Select the correct pre-filled KwikPen
Select the pen labelled with the correct weekly dose.
Check that the pen is not damaged, the expiry date has not passed, and the medicine is clear and colourless or slightly yellow.
Pull off the pen cap.
Wipe the red inner seal with an alcohol wipe.
Always use a new needle. Check the paper tab and outer needle cap for damage. Tear off the tab, push the needle onto the pen, and twist until secure.
Remove both needle caps.
Prime the pen. Slowly turn the dose knob until you hear two clicks and the extended line appears in the window. Point the needle upwards and gently tap the cartridge holder to collect air bubbles at the top. Press the dose knob until it stops and slowly count to 5. The 0 icon must appear and a small amount of medicine should leave the needle tip. If not, repeat up to two more times. On the third attempt, change the needle and try again. Make sure the dose knob is correctly set to the prime position and the needle is securely attached.
Step 2: Decide where to inject
Choose your stomach, at least 5 cm (2 inches) from your belly button, or the front of your thigh. If someone is helping, they can inject into your upper arm.
You can use the same body area each week, but not the exact same spot.
Check that there is no visible break or damage to the skin.
Clean the area with an alcohol wipe and allow it to dry.
Step 3: Inject your dose
Turn the dose knob until it stops and the 1 icon appears in the window.
Position the pen at the injection site so you can see the window.
Push the pen firmly against your skin and apply continuous pressure.
Press and hold the dose knob until it stops, then count to 5. The 0 icon should be visible before you remove the needle.
Remove the needle. If blood appears, press lightly with a clean tissue without rubbing.
A clicking sound during the injection is normal and indicates that the pen is working. After the injection, make sure the dose dial can still turn for your next dose.
Step 4: After the injection
Guide the needle tip into the outer cap on a flat surface without touching either one. Once covered, push the outer cap completely on.
Unscrew the needle and place it in your sharps bin.
Never replace the inner needle cap, as you may prick yourself.
Dispose of the needle immediately. Never store the pen with the needle attached.
Replace the pen cap after each use to protect Mounjaro from light.
Always take this medicine exactly as prescribed. Check with a Numan clinician if you are unsure.