Decoding Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

The UK is witnessing a significant shift in obesity management as powerful new weight-loss medications, Mounjaro and Wegovy, become more widely accessible. While promising substantial weight reduction, these drugs, now available through GPs for some patients and specialist clinics for others, come with important considerations regarding their use, effectiveness, and the unprecedented demand they are generating.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

Currently, two key injectable drugs are leading this revolution: semaglutide (marketed as Wegovy) and tirzepatide (sold as Mounjaro). Semaglutide is also the active ingredient in Ozempic, a medication used to treat type 2 diabetes. Both are administered via weekly, self-injectable pens into the upper arm, thigh, or stomach, typically starting at a low dose and gradually increasing to a maintenance level.

The Science Behind the Suppressed Appetite

These drugs work primarily as appetite suppressants by mimicking natural gut hormones.

Wegovy (semaglutide): Mimics glucagon-like peptide-1 (GLP-1), an intestinal hormone released after eating that promotes feelings of fullness and satiety.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

Mounjaro (tirzepatide): Goes a step further by mimicking both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP). GIP plays a role in metabolism and energy balance, providing an additional mechanism for regulating weight.

What Are the Weight Loss Results?

Patients typically begin to see weight loss within a few weeks of starting treatment. Recent head-to-head trials suggest Mounjaro might offer greater efficacy:

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

A study funded by Mounjaro's manufacturer, Eli Lilly, involving 750 obese individuals with an average weight of 113kg (nearly 18 stone), showed Mounjaro users achieved an average 20% weight reduction after 72 weeks of treatment.

In comparison, Wegovy users in the same trial experienced an average 14% weight reduction.

Previous clinical studies for Wegovy, when combined with diet, exercise, and behavioral support, showed users could lose more than 10% of their body weight after a year. Other trials for Mounjaro have indicated potential weight loss of up to a fifth of body weight.

Crucially, experts warn that users of both drugs tend to regain most of the lost weight once treatment is stopped, underscoring the importance of concurrent lifestyle changes.

Navigating NHS Access and Eligibility

The availability of these drugs on the NHS in England is expanding, but strict criteria apply, and services are grappling with immense demand.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

Wegovy is currently available on the NHS in England, Wales, and Scotland, prescribed by a weight management specialist. To qualify, adults must have a BMI of at least 35 (obese) and at least one weight-related health condition (e.g., high blood pressure). Individuals with cardiovascular disease who are overweight (BMI 25-29.9) but not yet obese may also qualify. NHS guidelines recommend it for a maximum of two years alongside diet and physical activity programs.

Mounjaro became available from specialist NHS weight-loss clinics in England and Wales in March 2025. As of June, some GPs in England have also begun offering it to eligible NHS patients who meet very specific criteria:

A BMI of 40 or over.

Or a BMI of 37.5 or over if from a minority ethnic background.

And four out of five of the following co-existing conditions: type 2 diabetes, high blood pressure, heart and vascular disease, high cholesterol, and obstructive sleep apnea.

Patients prescribed Mounjaro will also receive ongoing support, including regular checkups, exercise guidance, and healthy eating advice. Approximately 3.4 million people could eventually qualify for Mounjaro in England. However, the National Institute for Health and Care Excellence (NICE) cautions that it could take over a decade to roll out access to everyone who might benefit due to infrastructure and capacity challenges.

In a separate development, the government has announced plans to offer weight-loss jabs to unemployed individuals in England struggling with obesity, a move Prime Minister Sir Keir Starmer believes could significantly benefit both the economy and individual health.

Private Market and Safety Warnings

Both Wegovy and Mounjaro can be purchased privately from regulated sources such as supermarkets, chemists, and high-street clinics. Pens typically range from £200 to £300, depending on the dosage. However, regulatory bodies strongly advise against purchasing these drugs from unregulated online sources. A BBC investigation in November 2023 exposed online sellers offering semaglutide without prescriptions and even in beauty salons.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

Following these concerns, new guidance introduced in February 2025 mandates stricter checks for online pharmacies, including in-person or video consultations and verification of BMI via GP or medical records, to prevent those at a healthy weight or with a history of eating disorders from accessing the jabs.

Side Effects and Long-Term Use

The most common side effects associated with these weight-loss injections include nausea, vomiting, bloating, constipation, and diarrhea. Some users have also reported hair loss. While many find these side effects manageable and transient, others discontinue the drugs due to discomfort. Experts warn that complications can be more severe if the drugs are misused, such as for quick weight loss in individuals who are not clinically obese, or if obtained from unregulated sources. Rare but serious side effects can include gallbladder and kidney problems and depression. Hundreds of reports of pancreatic issues have also emerged, though a direct causal link to the medicines has not been confirmed.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

As users often regain weight after discontinuing treatment, specialists emphasize that these drugs should be integrated into a comprehensive program that includes consistent exercise and healthy eating habits.

Understanding Obesity and BMI

Obesity is defined as having excess body fat. In the UK, it is estimated that one in four adults is obese. The Body Mass Index (BMI) is the standard tool for categorizing weight, calculated by dividing an adult's weight in kilograms by the square of their height in meters.

Weight-Loss Wonders: How Mounjaro and Wegovy Are Changing the Obesity Landscape

BMI Categories for most adults:

Below 18.5: Underweight

18.5 to 24.9: Healthy weight

25 to 29.9: Overweight

30 to 39.9: Obese

40 or above: Severely obese

Important Note for Minority Ethnic Backgrounds: Individuals of Asian, Chinese, Middle Eastern, Black African, or African-Caribbean family backgrounds have a different BMI threshold for overweight and obesity due to differing health risks:

23 to 27.4: Overweight

27.5 or above: Obese

While BMI has limitations (e.g., it doesn't distinguish between muscle and fat), it remains a valuable general indicator of healthy weight for most individuals. For specific health concerns, always consult a doctor.