It only arrived in the UK a little over 20 months ago, but since its release, Mounjaro has transformed the market for GLP-1 medicines, with more than half of the 1.5 million people taking weight-loss drugs in the UK on the drug.
Dubbed the “King Kong” of weight-loss medication, Mounjaro, the brand name for tirzepatide, has helped almost a third of people lose a quarter of their bodyweight, according to a trial presented at the European Congress on Obesity this year.
Its rival, Wegovy, saw just 16 per cent of users achieve the same results.
Mounjaro is available on the NHS, although 90 per cent of users get their syringes containing four measured weekly doses through weight loss management plans at pharmacies on the high street, or online.
It only takes filling out a questionnaire, followed by an approval from a doctor for the drug to be prescribed.
But users face problems on the horizon, with manufacturer Eli Lilly announcing it will raise prices by 170 per cent from Monday, 1 September.
And with the price hike leading to a surge in demand, some pharmacists are suggesting people switch to Wegovy – but what is the difference, are the side effects different and will it have the desired impact?
Can I safely switch from Mounjaro to Wegovy?
The answer is yes, but anyone switching drugs as part of their weight-loss management plan should check with their doctor first.
If the doctor confirms the drug is suitable, then a starting dose would be suggested based on the amount being taken from Mounjaro.
Users must, however, wait seven days between their last Mounjaro injection and Wegovy jab.
The drug is available, like Mounjaro, through pharmacists.
Asda’s online pharmacy states: “Switching from Mounjaro to Wegovy is straightforward, but you must follow the correct steps to stay safe.”
How much does Mounjaro cost compared to Wegovy?
Wegovy is also self-administered through weekly injections, but dosages are smaller, which is reflected in the lower prices.
At Boots online pharmacy, the current monthly cost for Wegovy’s lowest dosage of 0.25mg a week is £139, rising to £228.89 for the highest dosage of 2.4mg.
At the same pharmacy for Mounjaro, the monthly cost of the lowest dosage of 2.5mg is £219, going up to £249 for the highest dosage of 15mg.
However, the price of Mounjaro will increase from Monday, 1 September.
At Boots, the new price for Mounjaro will be £177.30 for a month’s supply of 2.5mg, and £335 for 15mg.
What are the side effects of Mounjaro and Wegovy?
The drugs work similarly, but have some differences, such as active ingredient, dosage schedule, and manufacturer.
Both suppress a user’s appetite by activating a receptor called GLP-1 to send signals to the brain on hunger, slow down the emptying of the stomach and reduce blood sugar levels.
Mounjaro also contains ingredients that activate a receptor called GIP, which helps prevent fat from building up.
But as with any drug, there can be side effects.
Very common side effects for Mounjaro are: nausea, diarrhoea, vomiting and constipation.
For Wegovy, they are: nausea, diarrhoea, vomiting, constipation, headache, stomach pain and feeling weak.
Common side effects for Mounjaro are: dizziness, stomach pain, reflux, hair loss, gallstones, allergic reaction, low blood pressure, feeling tired, increased levels of pancreatic enzyme lipase in blood and increased calcitonin levels in blood
Common side effects for Wegovy are: dizziness, stomach pain, reflux, hair loss, gallstones and an inflamed stomach.
Mounjaro or Wegovy, which works better?
The first head-to-head trial of both weight-loss drugs showed that Mounjaro was more effective, although, with both drugs, there are concerns that users put the weight back on after coming off the jabs.
The research, funded by Mounjaro’s manufacturer Eli Lilly and presented at the European Congress on Obesity in Malaga, showed 32 per cent of people lost a quarter of their body weight on Mounjaro compared to 16 per cent on Wegovy.
It also showed that those on Mounjaro had better blood pressure, blood sugar and cholesterol levels.
However, the National Institute for Health and Care Excellence (Nice), the UK’s health watchdog, has raised concerns about patients regaining weight after stopping taking weight-loss drugs.
It has said that those coming off the medication should be offered "structured advice and follow-up support" to mitigate weight gain.
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