Weight Loss Medications in the UK: How They Work, Effects, and What to Expect

In recent years, medications for weight management have become a significant part of conversations around obesity and metabolic health. In the UK, Wegovy (semaglutide) and Mounjaro (tirzepatide) are now available for certain people, while Ozempic (another semaglutide-based drug) is primarily used for type 2 diabetes.

These drugs are not a magic solution, but they represent a new approach to supporting people with overweight and obesity. Understanding how they work, what research suggests, and how they interact with the body - including muscle and metabolism - is important for anyone exploring weight management strategies.

We're not suggesting anyone should or shouldn't take these medications. This blog is purely to provide information about what these drugs do, how they work, and what people in the UK should know from a health and fitness perspective.

How Wegovy, Mounjaro and Ozempic Work for Weight Loss

Understanding GLP-1 and GIP Medications in the UK

Wegovy and Mounjaro belong to a class of drugs called GLP-1 receptor agonists. GLP-1, short for glucagon-like peptide-1, is a hormone naturally produced in the gut that helps regulate appetite and blood sugar. These medications mimic this hormone, sending signals to the brain that reduce hunger, promote feelings of fullness, and slow the rate at which food leaves the stomach.

Mounjaro is slightly different because it also targets another hormone, GIP (glucose-dependent insulinotropic polypeptide). GIP worked alongside GLP-1 to improve insulin regulation and reduce fat storage in the body. This dual action may enhance overall weight management outcomes by not only controlling appetite but also supporting metabolic processes that reduce fat accumulation.

How These Weight Loss Injections Are Administered

In the UK, access to these medications is carefully regulated. Adults with a body mass index (BMI) of 30 or above, or 27 or above with weight-related health conditions such as high blood pressure or prediabetes, may qualitfy under NHS guidance. Private clinics may offer access more flexibility, but it is essential to ensure that medications come from regulated and safe sources. The medications are administered as weekly injections, with dosage adjustments over time under the supervision of healthcare professionals.

Outcomes and Effects of Weight Loss Medications

Realistic Weight Loss Results: Trials vs Everyday Life

Clinical trials for Wegovy and Mounjaro have reported impressive results. The STEP-1 trial showed that participants taking Wegovy 2.4mg once weekly over 68 weeks lost an average of 15 to 17 per cent of bodyweight, with roughly 85 percent achieving at least 5 percent reduction in starting weight. The SURMOUNT-1 trials found that Mounjaro users over 72 weeks lost up to 22.5 percent of body weight at the highest dose, with more than 89 percent reaching at least 5 percent loss.

While these numbers are encouraging, they do not automatically translate to real-world outcomes. Clinical trials are highly controlled: participants follow strict diet, receive frequent support, and are closely monitored. Daily life introduces challenges that trials don't account for, including emotional eating, irregular schedules, social events, and stress. In real-world UK settings, most people using these medications see smaller average weight losses. Data suggest that those who maintain medication for a year may lose around 11.9 percent of their body weight, while those who discontinue early may lose 3.6 percent, and stopping between three and twelve months typically results in around 6.8 percent weight loss.

Side Effects and Tolerability

Side effects are common but usually manageable. Gastrointestinal symptoms - nausea, vomiting, diarrhoea, and fatigue - are the most frequently reported. They are often mild to moderate and tend to improve over time or with dosage adjustments. Rare but serious side effects, such as pancreatisis, are possible, making medical supervision essential.

Muscle Mass, Lean Tissue, and Overall Health

While weight loss is often the main focus, it is equally important to consider muscle and lean tissue. Lean mass includes not just muscles, but also bones, organs, and water - tissues that are metabolically quite active and essential for maintaining strength, energy, and long-term health. Research indicates that when using medications like Wegovy or Mounjaro, approximately 25-39 percent of total weight lost can come from lean mass. The exact proportion varies depending on individual factors, the amount of weight lost, and the approach used, and is broadly comparable to other weight loss strategies such as diet or lifestyle interventions.

Maintaining muscle during weight loss is critical for several reasons. Muscle tissue burns more calories at rest than fat, helping to support a healthy metabolism and making it easier to sustain weight loss over time. Muscle also underpins physical strength and functional mobility; losing too much can lead to fatigue, reduced performance in daily activities, and an increased risk of injury.

From a broader health perspective, reduced muscle mass can have implications beyond strength. Studies suggest that significant lean mass loss may impair immunity, affect glucose regulation, and contribute to conditions like sarcopenic obesity - a combination of low muscle mass and excess body fat - which is associated with higher risks of cardiovascular disease and other adverse health outcomes.

There are practical strategies to help protect muscle while using weight loss medications:

• Strength and resistance training: Regular exercise targeting all major muscle groups stimulate muscle growth and help maintain existing tissue

• Adequate protein intake: Consuming 1.6-2.2 grams of protein per kilogram of body weight per day supports muscle repair and growth.

• Monitoring progress: Tracking strength, energy, and performance can help identify when adjustments in exercise or nutrition may be needed.

Planning for Life After Weight Loss Medication

Maintaining Weight Loss and Healthy Habits

Using medications like Wegovy or Mounjaro can be highly effective for supporting weight loss, but their benefits are maximised when combined with sustainable lifestyle strategies. Clinical trials show significant weight reduction while medication is ongoing, yet stopping treatment may result in partial weight regain if long-term habits are not established. Real-world experience in the UK demonstrates that some people can maintain a portion of their weight loss by continuing healthy eating, exercise, and behavioural strategies are discontinuing medication.

It's important to view these medications as supportive tools rather than standalone solutions. Developing habits that can be maintained independently of the medication is crucial for long-term success.

Additionally, planning for life after medication should include realistic expectations and flexibility. Weight maintenance is rarely perfectly linear; minor fluctuations are normal. Understanding this helps reduce frustration and supports a long-term mindset. Some people may choose to pause and later resume medication under medical supervision if weight begins to creep back, while others may switch to alternative therapies or non-pharmacological approaches.

In essence. successful long-term weight management relies on creating habits and routines that persist beyond the medication itself.