Mounjaro is now available for prescription in the UK. 

Mounjaro (which contains the active compound tirzepatide) is the latest weight loss drug to receive UK regulatory approval, and subsequently hit the shelves of private pharmacies and also for a select number of patients via the NHS. Mounjaro is similar to other weight loss drugs that have come before it, like Wegozy and Ozempic, but not exactly the same. 

This leaves patients with a big question to answer—should I take Mounjaro or Wegovy? And, importantly, which is more effective? For those deciding between the two weight loss medications, we’ll compare Mounjaro and Wegovy, breaking down the results from trials that have compared these two medications.

The differences between Mounjaro and Wegovy

Before we dive into the efficacy of these two medications, it’s first worth understanding the difference between Mounjaro and Wegovy. While both are taken via a weekly injection pen and both approved for the treatment of obesity in the UK, there are important differences to note.

Mounjaro is the brand name for a medication called tirzepatide. Tirzepatide is a dual GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) agonist, meaning it combines the effects of the two different compounds (which we’ll go into shortly). Wegovy, meanwhile, is the brand name for semaglutide, which is a GLP-1. Semaglutide is also known by the brand name Ozempic, however Ozempic is licensed for the treatment of type 2 diabetes, rather than obesity.

So what do all these compound acronyms actually mean in terms of what differentiates these medications?

Let's start with similarities. Both GLP-1 and GIP are naturally occurring gut hormones called incretins. Incretins are released in response to nutrient intake, and stimulate the secretion of insulin, which kicks off a whole series of events related to how your body turns food into nutrients to be used in various ways. GLP-1 and GIP medications work by mimicking the natural hormones and thereby activating the receptors for these incretin hormones.

Researchers are still trying to understand the full mechanism of action of these compounds, and the effects they have on the body, but it is clear that they impact a wide range of internal procesed, from fat and bone formation to how the brain controls appetite.[1]

The dosage also differs between these two medications, though it's worth noting that because they are different compounds the dosages should not be compared side by side. Mounjaro starts at 2.5mg for the first four weeks, and then can be increased monthly to 5mg, 7.5mg, 10mg, 12.5mg, and 15mg. Wegovy, meanwhile, starts at 0.25mg for weeks 1 to 4, then subsequently to 0.5mg, 1mg, 1.7mg, and 2.4mg. Dosage decisions should be made between yourself and your prescriber based on how your body reacts to the medication, and some people may choose to stay on lower doses if they are experiencing side effects or already seeing promising results.

Mounjaro and Wegovy: Which is more effective?

If you are comparing the efficacy of Mounjaro and Wegovy, the best place to look is at the results from trials that have compared the two within the same trial.

SURPASS-2 was one of the original studies comparing the two medications, although in this instance in patients with type 2 diabetes. While the main point of comparison of the trials was impact on blood sugar levels, the trial also found that Mounjaro helped patients achieve average weight loss of between 7.6kg to 11.2kg, compared to 5.7kg for semaglutide. It's worth nothing that only semaglutide 1mg was studied in this trial, whereas the maximum dosage of tirzepatide was 15mg.[2]

Another study published in 2023, also in patients with type 2 diabetes, showed that tirzepatide was once again superior in terms of weight loss outcomes[3]. After 72 weeks, tirzepatide resulted in an average 17.8% weight loss, compared to semaglutide which led to just 12.4% weight loss. In this case, patients were on the maximum doses of both medications (2.4mg semaglutide and 15mg tirzepatide).

The results of an additional study were published late in 2023, comparing tirzepatide and semaglutide for weight loss in overweight and obese adults. Crucially, this study has not yet been peer reviewed, meaning it should not be used to guide clinical practice—but the results are fairly emphatic. 42.3% of those taking tirzepatide had lost at least 15% of their weight, in comparison to just 19.3% when taking semaglutide. [4]

While they cannot be compared directly, there are also studies investigating weight loss outcomes with each of these medications. The seminal trials for semaglutide and tirzepatide in patients with obesity found that the medications lead to an average of 15% and 21% body weight loss, respectively.[5,6]

Can I purchase Mounjaro in the UK?

If you are looking to try Mounjaro for weight loss in the UK, you have a number of options. 

Mounjaro has recently been made available on the NHS for a limited number of patients with type 2 diabetes and obesity. At present, most people will be unable to access Mounjaro through the NHS, in which case a private prescription would be the next port of call.

The simplest way to purchase Mounjaro privately is through an online pharmacy or digital health provider. Habitual, for instance, offers a Mounjaro prescription that starts from £199 a month, which comes with a custom-built habit change and tracking app, regular virtual checkups, and access to a peer support WhatsApp group.

When deciding which weight loss medication you should look for a prescription for, there are many factors to weigh up—cost, ease of access, and so on. As there are no differences in eligibility criteria between the two medications, it is ultimately your decision as to which medication you choose.