A comprehensive guide to GLP-1 weight loss injections—how they work, comparing Wegovy and Mounjaro, clinical trial data, side effects, eligibility, and safe access in Surrey.
March 2026 | 10 min read | Lambert Medical Practice Clinical Team
Weight loss injections like Wegovy and Mounjaro have generated enormous interest in recent years, with celebrity endorsements and waiting lists across the UK. These medications represent a genuine advance in weight management for people with obesity or weight-related health problems. But separating marketing hype from medical reality is crucial. At Lambert Medical Practice in Surbiton, we help patients understand what these injections actually do, whether they're suitable, and how to access them safely with proper medical supervision.
Both Wegovy and Mounjaro are based on GLP-1 (Glucagon-Like Peptide-1) agonist technology. GLP-1 is a naturally occurring hormone that regulates appetite, blood sugar, and metabolism. These medications mimic GLP-1's action in your brain and gut, creating multiple weight loss mechanisms:
Importantly, these injections don't work through stimulation or suppression of major organ function. They work on appetite regulation systems, making them fundamentally different from older weight loss medications. The result is that most people naturally eat less without feeling like they're "dieting."
Weight loss injections help suppress appetite and improve food choices, but they're not a complete solution. They work best combined with dietary changes, increased physical activity, and lifestyle modifications. People who continue eating excessive amounts despite reduced hunger, or who don't engage in lifestyle changes, will see limited benefit.
Wegovy is semaglutide, marketed specifically for weight loss (same drug as Ozempic, which is used for diabetes). The landmark trial for Wegovy is STEP (Semaglutide Treatment Effect in People with obesity):
STEP Trial Results (Primary Trial):
Dosing Schedule: Wegovy starts at 0.25mg weekly, increasing by 0.25mg every 4 weeks until reaching the maintenance dose of 2.4mg weekly. This gradual titration reduces side effects.
Mounjaro is tirzepatide, a dual GIP/GLP-1 receptor agonist. Rather than working solely on GLP-1, it activates both GIP (Glucose-dependent Insulinotropic Polypeptide) and GLP-1 receptors, providing potentially greater weight loss:
SURMOUNT Trial Results (Primary Trial):
Dosing Schedule: Mounjaro starts at 2.5mg weekly, increasing to 5mg, 10mg, and 15mg weekly. Titration is similar to Wegovy.
Comparative Effectiveness: The approximately 6% additional weight loss with Mounjaro (21% vs 15%) is modest but real. For some patients, this difference is meaningful; for others, the choice between drugs might depend on side effects, cost, or availability.
Both medications commonly cause gastrointestinal side effects, particularly during dose escalation:
| Side Effect | Frequency | Management |
|---|---|---|
| Nausea | Very common (30–50%) | Usually improves after 1–2 weeks at each dose; eating smaller meals helps |
| Vomiting | Common (10–25%) | Usually mild and reduces over time; stay hydrated |
| Diarrhoea or constipation | Common (20–40%) | Dietary fibre, hydration, and sometimes antidiarrhoeal or laxatives help |
| Abdominal discomfort | Common | Usually mild; improving as body adjusts |
| Loss of appetite | Desired effect | Intended action; ensures adequate nutrition despite reduced intake |
| Fatigue or dizziness | Occasional | Often related to rapid weight loss or inadequate nutrition; ensure adequate protein and calories |
| Gallstones | Rare but serious | Associated with rapid weight loss; discuss symptoms (severe upper abdominal pain) with doctor immediately |
Most side effects improve within days to weeks as your body adjusts. The gradual dose escalation significantly reduces side effects. Taking injections with smaller, lower-fat meals and staying hydrated helps tremendously.
Medical guidelines recommend weight loss injection therapy for:
Age, ethnicity, and general health matter less than the BMI threshold and weight-related complications. However, certain conditions make these medications unsuitable.
This is crucial to understand: weight loss injections work only whilst you're using them. When you stop taking the medication, appetite hormones gradually normalise, and weight typically returns over months. Research shows that after stopping:
This means weight loss injections are typically long-term treatments. Most patients continue indefinitely, similar to medications for blood pressure or diabetes. This has significant cost implications and underscores why lifestyle changes are essential—they provide the foundation for sustained weight loss after treatment ends.
Weight loss injections are not routinely available on the NHS, except for patients with type 2 diabetes (where semaglutide is used as diabetes medication). For weight loss alone, private prescription is necessary. Costs typically range from £150–250 per month for private prescriptions, varying by pharmacy and supplier. Treatment usually runs 6–12 months minimum.
At Lambert Medical Practice, we provide comprehensive assessment and can issue private prescriptions if appropriate. This ensures you're genuinely suitable, understand realistic expectations, and receive ongoing monitoring during treatment.
Obtaining these medications safely requires:
Buying these medications online without medical assessment is risky—you might have contraindications, drug interactions, or metabolic conditions making them unsafe.
Mounjaro causes slightly greater weight loss (21% vs 15%), making it potentially more effective. However, "better" depends on individual factors: tolerability of side effects, personal preference, cost, and availability. For some patients, Wegovy's slightly milder side effect profile appeals more. A GP can help determine which suits your circumstances better.
Potentially, but this requires careful medical planning. Weight loss injection plus bariatric surgery carries unique risks—rapid weight loss, nutritional deficiencies, medication interactions. Your GP and bariatric surgeon must coordinate. Generally, GLP-1 injections are tried first, with surgery considered if insufficient weight loss occurs.
Significant weight loss (20+ kg) often leaves loose skin, particularly around the abdomen, arms, and thighs. This doesn't improve with continued injection use and typically requires cosmetic surgery (body contouring). This is an important consideration for realistic expectations and planning.
If you're considering weight loss injections and want proper medical assessment, realistic information, and ongoing supervision, Lambert Medical Practice in Surbiton offers comprehensive evaluation. We'll discuss whether these medications are appropriate for you, explain realistic expectations, arrange necessary blood tests, and if proceeding, provide proper monitoring and support throughout treatment.
Ready to explore weight loss treatment options? Book an appointment today for a detailed consultation. We offer same-day appointments and can arrange blood tests immediately, so you get answers quickly.
Have questions about this topic? Speak to one of our experienced GPs.
Book Appointment 0208 133 5694Book an appointment at Lambert Medical Practice in Surbiton. Same-day appointments available.