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The revolutionary new treatment for weight loss available now from Semapen
(part of the Phoenix Health group)

Important: On the advice of the manufacturer and the MHRA (Medicines and Healthcare products Regulatory Agency) all current UK supplies of 2.5mg Mounjaro®️ pens with an original expiry date of May 24 are now considered safe to use until October 2024.

About Mounjaro

Mounjaro (also known as tirzepatide) is the latest in a class of weight loss injections that are proven to dramatically reduce weight and the severity of type 2 diabetes.

Like Wegovy (semaglutide), Mounjaro mimics the effects of natural hormones called incretins that control hunger, appetite, and blood sugar levels. 

The key difference in the way Wegovy and Mounjaro work is that Wegovy mimics the effect of one of the three main incretin hormones in the body (GLP1), whereas Mounjaro is a ‘Twincretin’ that mimics the effect of two (both GLP1 and another called GIP). 

This ‘Twincretin’ double effect of Mounjaro was shown to produce an average of 21% weight loss, compared to about 15% with Wegovy.

How Mounjaro Works

The Science of Weight Loss

Mounjaro has three distinct actions:

Suppresses Appetite:

Mounjaro stimulates GLP-1 and GIP receptors, which reduces the desire to eat and creates a feeling of early fullness. This makes it easier to control your appetite, portion size, and hunger pangs.

Boosts Metabolism:

Mounjaro stimulates insulin release, which controls blood sugar and enhances the body’s metabolism, promoting energy expenditure and contributing to weight loss.

Reduces dangerous visceral (‘belly’) fat:

As you lose weight on Mounjaro, for everyone part of lean (muscle) mass lost, patients lose 3 times as much fat mass, particularly the more dangerous visceral ‘belly’ fat that is associated with heart disease and diabetes. 

Suppresses Appetite

Boosts Metabolism

Reduces visceral fat

Lose Weight with Mounjaro

You can expect to lose an average of 21% of your body weight (mostly within 3 months) and maintain this for up to 72 weeks if you continue on treatment.


Compare Mounjaro vs Wegovy:






Active ingredient Tirzepatide   Semaglutide
Mechanism of Action Stimulates GLP-1 and GIP action   Stimulates GLP-1 action
Dosage Once weekly injection   Once weekly injection
Number of months to reach the maximum dose 6   5
Average Weight Loss (non-diabetic) 21%   15%
Side Effects Similar to Wegovy but with less nausea.

Hair thinning (temporary)- daily multivitamins advised

Interferes with the action of the oral contraceptive pill.

 Nausea, constipation,     diarrhoea, vomiting, acid reflux, belching, and bloating are the most   common.



Availability in the UK Available   Available



Want to Learn More about Mounjaro?

Mounjaro (also known as Tirzepatide) is considered to be the most effective non-surgical treatment for weight loss. Clinical trials have also demonstrated significant reductions in blood sugar levels, blood pressure, and cholesterol with Mounjaro compared to those receiving dietary support and a placebo. Its mechanism of action involves activation of both GLP-1 and GIP receptors. These receptors, (located in the brain, liver and muscles), play key roles in regulating appetite, food intake, energy expenditure, and glucose metabolism. As with any medication, there are potential side effects associated with Mounjaro, including gastrointestinal symptoms such as nausea and diarrhoea, which are common with all GLP-1 receptor agonists. However, overall, it has demonstrated a favourable safety profile and is well-tolerated.

How to Inject Mounjaro (Tirzepatide)

Mounjaro  is given as a small injection under the skin of your tummy or thigh, because this works much better than tablets.  The good news is that the injection is just given once a week!   We recommend injections are placed about two inches away from the belly button area or in the upper leg (thigh). Try to switch the site of injection every week to minimise the chances of injection site infections.

Each Mounjaro pen is already filled with enough of the medication to last you a month, with a little bit to spare.  So that’s 4 doses in one pen.  You simply have to dial up a full dose by twisting the pen, attach one of our ultra fine needles and off you go!  The needles are so fine that most injections are painless.

The pen can be used at any time of the day, with or without meals, but you should always use it on the same day each week if you can.

Click here to download the instructions for use on how to inject Mounjaro KwikPen 


What Strength Pen Should I Buy?

Mounjaro pens come in different strengths that contain either 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, or 15 mg per dose.  The idea is to start at the lowest dose and gradually build up to higher doses each month, one step at a time until you find the dose that suits you best. You don’t need to keep your pen in the fridge because it’s fine at room temperature for about 5 weeks, by which time you will be ready for your next pen.

It’s about getting a balance between great weight loss and minimal side effects.  Slowly stepping up the strength of each pen once a month gives your body time to get used to the drug and keeps the risk of side effects to a minimum.



So here is what a typical treatment programme with Mounjaro looks like:

  • Weeks 1-4: 2.5 mg once a week
  • Weeks 5-8: 5 mg once a week
  • Weeks 9-12: 7.5 mg once a week
  • Weeks 13-16: 10 mg once a week
  • Weeks 17-20: 12.5 mg once a week
  • Weeks 21 onwards: 15 mg once a week

Visit our blog on Mounjaro Cost in the UK for detailed information about the Mounjaro injection price in the UK.

You can download and read the patient information leaflets (PIL) for each dose of Mounjaro here:

Patient information leaflet.

Convenience at Your Fingertips:

At Semapen, we’ve designed everything to make life as easy as we can for you, so there’s no need to worry about remembering to re-order your next weight loss pen and which dose it should be – our subscription service takes care of all of that for you.

Going on holiday and want to pause your weight loss programme? No problem – just drop us a message through the Semapen app and we’ll set things up so your new pen arrives when you return.

If you’re doing well on a pen strength that suits you, there’s no need to automatically step up to a stronger pen if you’d prefer not to. Log in to the Semapen app and you can choose to lock in at the same pen dose for as long as you want.

If you would like to learn more about Mounjaro, read our Mounjaro blogs here.


Medically Reviewed By: Professor David Kerrigan, MD, FRCS, FRCSEd, MBChB
Last Reviewed: 24/04/2024