Mounjaro is now approved for weight loss in the UK and studies have shown that it may be more effective than Wegovy for weight loss. If you’re taking Wegovy, we’ve got you covered—here’s a simple guide to switching between the two medications.

Mounjaro vs. Wegovy

The main difference between Wegovy and Mounjaro is their composition. Wegovy contains a compound called semaglutide, whereas Mounjaro contains one called tirzepatide.

Both semaglutide and tirzepatide fall under the category of GLP-1 (glucagon like peptide 1) agonists.  They work by imitating natural hormones, incretins, produced by the gut after eating to stimulate insulin secretion, slow gastric emptying and reduce glucose produced by the liver when not needed.  This causes various effects in the body including appetite suppression and prolonged feeling of fulness.

While semaglutide is just a GLP-1, tirzepatide is a dual-agonist, as it also contains another incretin called glucose-dependent insulinotopic polypeptide (GIP). The GIP component adds extra benefits, such as reducing fat accumulation, improving bone density, and decreasing stomach acid secretion.

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Clinical trials on Mounjaro vs. Wegovy

There is no current research directly comparing the effectiveness of Wegovy to Mounjaro specifically for weight loss, however the manufacturer of Mounjaro, Eli Lilly, is currently planning a 78 week trial to directly compare the effectiveness of semaglutide and tirzepatide. This study [1] doesn’t end until November 2024, so we only have the individual trials by each manufacturer for now. It’s important to note that standalone trials aren’t necessarily an apples-to-apples comparison between two medications—as you really need a single trial comparing the medications in a controlled setting to evaluate their relative efficacy.

Novo Nordisk’s 68-week study reported an average weight loss of 15% [2] from once-weekly semaglutide. In comparison, Eli Lilly’s 72-week study reported an average weight loss of 21% [3] from once weekly tirzepatide. 

There is one side-by-side trial [4] in patients with type 2 diabetes that shows that tirzepatide results in slightly higher levels of weight loss than semaglutide, but again this is in a different patient group (those being treated for type 2 diabetes rather than obesity).

Can you switch from Wegovy to Mounjaro on a higher dosage?

At the moment, there is no data or guidance from the manufacturer on switching from Wegovy (semaglutide)onto a higher dose of Mounjaro (tirzepatide), so the recommendation is to start on the lowest dosage of Mounjaro 2.5mg.

It's important to bear in mind that semaglutide and tirzepatide are different compounds, so even though you'll start at the lowest dose of Mounjaro you won't be starting from scratch. There may be guidance available in the future for switching between medications at a higher dosage, and we will update our guidance accordingly as and when this research is published.

Why switch from Wegovy to Mounjaro?

The primary reason for switching from Wegovy to Mounjaro is that Mounjaro may lead to greater levels of weight loss. But, as mentioned above, we don’t yet have a head-to-head comparison between the medications so it’s hard to say for sure that Mounjaro leads to higher levels of weight loss. Further, everyone will react differently to different medications, so there’s no way to know what your unique response will be.

Furthermore, if you’ve reached a weight plateau on Wegovy, you may want to give Mounjaro a try. If you are on the highest dose and haven’t reached your weight loss goal, tirzepatide might help you break through a plateau. However you have to remember that neither Wegovy or Mounjaro are a "quick fix" and both of these medications are designed to be used alongside lifestyle interventions and behaviour change.

Another consideration is the side effects you experience on weight loss medication. Mounjaro and Wegovy have a very similar side effects profile as they work in similar ways, however as with the level of weight loss, every individual responds differently, so it’s possible that your side effects could differ between the two medications. In both cases, it’s important to follow the titration schedule and dosage instructions to minimise side effects..

Finally, cost is an important factor if you’re buying Wegovy or Mounjaro privately. Early pricing information puts both drugs at very similar, if not the same cost for the initial doses. At Habitual both medications start at £229 and increase with the dosage, and you can choose whether to stay on your current dose or escalate to the next one every 4 weeks.

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How to switch from Wegovy to Mounjaro

It’s important to work with your healthcare provider when considering any medication switch. Wegovy and Mounjaro should not be used at the same time and you would need to completely stop Wegovy first before starting Mounjaro. You should also take a short break between medications to allow the semaglutide to leave your system before injecting tirzepatide—7 days from your last injection of Wegovy is our prescriber's current recommendation.

Steps:

1. Take your last Wegovy injection and safely discard your injection pen.
2. Wait for at least one week.
3. Take your first 2.5mg Mounjaro injection.

While it may be tempting to start on a higher dose of Mounjaro if you’ve already titrated up to high strength Wegovy, the manufacturer guidance is to start from the lowest strength Mounjaro pen. Remember that the two medications, whilst similar, contain different compounds, so it’s not quite as simple as swapping one out for the other.

In conclusion, Mounjaro may be more effective for weight loss, but there is no direct research comparison between it and Wegovy.  If you are happy and settled on Wegovy then you may wish to continue on this, as each patient will respond differently to any medication.

If you are looking to switch, check your eligibility today.