Mounjaro® Injectable Pen

Mounjaro contains the active ingredient tirzepatide, which has a dual mechanism of action as it mimics both the GLP-1 and GIP hormones in the body to aid weight loss.

• Mounjaro activates GLP-1 receptors to slow down gastric emptying and promote insulin secretion when blood sugar levels are elevated. This helps with feeling fuller for longer and regulates food cravings to support weight loss.
• Mounjaro also activates GIP receptors to further boost insulin secretion and improve fat metabolism, supporting weight loss.

It can take 1–2 weeks up to a few months to experience noticeable weight loss with Mounjaro, depending on factors such as the individual’s diet, lifestyle, starting weight, dosage escalation, tolerability to treatment and how consistent they are with following the prescribed dosage schedule.

Individuals who follow the dosage schedule and maintain a balanced, calorie-restricted diet as part of a healthy lifestyle are likely to experience the desired results from using Mounjaro sooner.

If you stop taking Mounjaro, the effects of the medication on appetite regulation will decrease, which could cause you to overeat and regain some of the weight lost during treatment.

Mounjaro has been approved by the UK Medicines and Healthcare Regulatory Agency as a safe and effective weight loss medication.

To maximise the safety of Mounjaro, please read the Mounjaro Patient Information Leaflet before use and always follow the prescribed dosage schedule.

Recommended reading: Mounjaro Side Effects: What They Are & How To Manage Them

Mounjaro should be taken once a week at the same time each day, following the prescribed dosage escalation schedule.

You should inject Mounjaro into your upper legs, stomach (abdomen), or upper arms.

We recommend injecting the first dose into the stomach (keeping a 5 cm distance from the belly button) as it has more fat and fewer nerves, making it easier and less painful to administer the dose.

Moreover, you should rotate between injecting the stomach (abdomen), upper arms and upper legs each week to reduce the risk of skin irritation.

Recommended reading: How To Take Mounjaro Injections

The starting dose of Mounjaro is 2.5mg injected once per week for four weeks.

If you do not experience side effects from taking the starting dose of the treatment, then you can increase your dose to 5mg per week for weeks 5 to 8.

Thereafter, you can continue to increase the dose in line with the table below, provided you are cleared to do so by a doctor or pharmacist.

Always take Mounjaro according to the dosage schedule and instructions provided to you by the prescriber.

Mounjaro and Wegovy are two different injectable weight loss medications with differing mechanisms of action.

Wegovy contains the active ingredient semaglutide, which mimics a hormone called GLP-1 to help regulate appetite and slow down stomach emptying.

Wegovy also improves insulin sensitivity, stabilising blood glucose levels and preventing sudden spikes and crashes to prevent excessive hunger signalling by the brain.

Mounjaro contains a different active ingredient, tirzepatide, which also mimics GLP-1, in addition to mimicking another hormone known as GIP to further enhance insulin release by the body.

Mounjaro is not the same as Ozempic. While both medications are prescribed for weight loss, they have different active ingredients and mechanisms of action.

Mounjaro contains tirzepatide, an active ingredient that mimics the gastric inhibitory polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) hormones. In contrast, Ozempic contains semaglutide, an active ingredient that mimics the GLP-1 hormone, but not the GIP hormone.

Orlistat is a clinically proven oral weight loss treatment that reduces total calorie intake by limiting the absorption of dietary fat.

In contrast, Mounjaro is a weight loss injection that works differently by stabilising blood sugar levels to reduce appetite and slowing stomach emptying, helping you feel fuller for longer.

Mounjaro and Zepbound are both medications containing the active ingredient tirzepatide, which mimics hormones to make the body feel fuller and reduce appetite.

Zepbound is the US name for the same weight loss medication, whereas in the UK, tirzepatide is licensed under the name Mounjaro.

The medications function in the same way and are both prescribed for weight loss and metabolic regulation.

Mounjaro can result in a loss of body fat, which may affect menstrual cycles in some women. This is due to the fact that menstrual cycles are affected by levels of the hormone oestrogen, which is produced by fatty tissues in the body.

Women who experience changes in menstrual cycles from taking Mounjaro are recommended to consult a doctor for further advice.

It is not advisable to take Mounjaro (tirzepatide) during pregnancy, as there is limited data on its safety and impact on developing children.

If you are pregnant or intend to become pregnant and have taken Mounjaro, discuss your usage of this medication with your doctor immediately.

• Tirzepatide once weekly for the treatment of obesity, 2022. [Accessed 4th July 2025]
• Electronic medicines compendium: Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen. [Accessed 4th July 2025]
• Eli Lilly & Company: Mounjaro Patient Booklet, 2025. [Accessed 4th July 2025]