Weight loss drugs are revolutionising how we treat obesity. Adult obesity has more than doubled since 1990. The World Health Organisation reports that over 2.5 billion adults worldwide were overweight in 2022. Each year, at least 2.8 million people lose their lives to obesity-related complications.
The results from Mounjaro are remarkable. Studies show patients can lose up to 20.9% of their body weight with the 15mg dose by week 72. GLP-1 drugs help patients shed more than 15% of their weight. These significant reductions can help improve serious health conditions linked to obesity. The UK’s National Institute for Health and Care Excellence (NICE) recognised these benefits and approved both semaglutide and tirzepatide for weight loss by October 2023.
This piece covers everything you should know about these groundbreaking treatments. You’ll learn how they work, who qualifies for NHS access, their effectiveness, possible side effects, and what new developments might come in 2026.
How the new weight loss drugs work
The latest weight loss medications mimic natural hormones in our digestive system. These breakthrough drugs target the body’s appetite control systems more effectively than older treatments that showed modest results.
GLP-1 and GIP: What they do in the body
GLP-1 (glucagon-like peptide-1) is a hormone our body releases after eating that plays several vital roles. It makes the pancreas release insulin, blocks glucagon secretion (which would raise blood sugar), slows down how fast our stomach empties, and makes us feel fuller by acting on brain regions that process hunger signals.
GIP (glucose-dependent insulinotropic polypeptide) is another hormone that comes out after meals. It balances energy through signals in the brain and fat tissue. GLP-1 mainly controls appetite and digestion, while GIP also affects how our body stores and processes fat.
How Mounjaro is different from Wegovy
Wegovy (semaglutide) works as a GLP-1 receptor agonist only. It mimics one hormone to help control blood sugar and appetite. This single-action approach reduces hunger and slows digestion.
Mounjaro (tirzepatide) takes a dual approach by targeting both GLP-1 and GIP receptors at once. It reduces appetite and slows stomach emptying, and helps stop fat buildup through its GIP action. Mounjaro uses two complementary mechanisms while Wegovy uses just one.
Why dual-action drugs work better
The dual-receptor approach creates cooperative effects. Clinical trials show that Mounjaro leads to more weight loss than single-action medications. People taking tirzepatide lost 19.5% of their weight with the 10mg dose and 20.9% with the 15mg dose, compared to 3.1% with placebo.
Head-to-head comparisons show tirzepatide gets better results. Patients on tirzepatide lost 15.3% of their body weight after 12 months in real-life applications, while those on semaglutide lost 8.3%. These results prove that targeting multiple hormone pathways at once works better.
The success of dual-action medications has led to development of even more advanced treatments. New triple-action drugs that target GLP-1, GIP and glucagon receptors at the same time might offer even better weight management options in the future.
Who can get these drugs on the NHS
The NHS will roll out these new weight loss medications starting June 2025, following strict eligibility criteria.
Eligibility criteria for Mounjaro and Wegovy
The NHS plans a careful three-year rollout of Mounjaro (tirzepatide). Patients with the highest clinical need will qualify first. Each patient must have a BMI of at least 40 kg/m² and show at least four of five specific weight-related health conditions. These conditions include:
- Type 2 diabetes
- Hypertension (high blood pressure)
- Cardiovascular disease
- Obstructive sleep apnoea
- Dyslipidaemia (abnormal blood fats)
Patients must also take part in lifestyle support programmes with their medication.
Wegovy (semaglutide) has different qualifying criteria. Patients need a BMI of 35 or higher (or 32.5+ for certain ethnic backgrounds) with at least one weight-related health condition. Some patients with a BMI between 30-34.9 (or 27.5-32.4 for specific ethnic groups) might qualify if they meet specialist weight management service requirements.
BMI thresholds and comorbidities
Different ethnic groups have varying BMI requirements. The threshold drops by 2.5 kg/m² for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. This change reflects the increased health risks these groups face at lower BMI levels.
Mounjaro’s rollout targets three specific groups over three years:
- Cohort 1 (June 2025): BMI ≥40 with four comorbidities
- Cohort 2 (June 2026): BMI 35-39.9 with four comorbidities
- Cohort 3 (April 2027): BMI ≥40 with three comorbidities
Why some people are still excluded
NICE has asked NHS England to focus on 220,000 patients during the first three years. Service capacity limits and healthcare staff training needs drive this careful approach.
Many patients with obesity don’t meet current eligibility guidelines. People with fewer health conditions or lower BMI measurements must wait for future phases. Some regions show varying implementation rates, and certain Integrated Care Boards haven’t set up prescribing pathways yet.
These medications cannot be used during pregnancy, breastfeeding, or when planning pregnancy. Women who could become pregnant must use contraception while taking the medication and for at least one month after stopping.
How effective are the new treatments?
Clinical trials show remarkable results for new weight loss drugs, but they come with key warnings about how well they work over time.
Average weight loss results from trials
These medications produced unprecedented weight reduction in clinical studies. Patients using Tirzepatide (Mounjaro) lost more weight than others, dropping an average of 20.2% body weight (22.8kg). Semaglutide (Wegovy) users lost 13.7% (15kg) during the same time. The major 72-week SURMOUNT-1 trial showed that tirzepatide worked based on dosage. People lost an average of 15.0% (5mg), 19.5% (10mg), and 20.9% (15mg) of their weight.
The number of people reaching major weight loss goals varied by a lot:
- 85-91% of tirzepatide users lost at least 5% body weight
- 50-57% dropped ≥20% of their weight
- 32-36% reached ≥25% weight loss with higher doses
How long it takes to see results
Patients usually notice changes in appetite within two weeks. The visible weight loss starts between weeks 4-8. Weight loss follows a clear pattern after that:
- By month 2: ~4% body weight
- By month 3: ~6% body weight
- By month 4: ~8% body weight
Best results usually appear around 72 weeks (18 months) of steady treatment.
What happens after stopping the drug
Stopping treatment makes people gain weight back steadily. Weight returns at about 0.8kg monthly with newer drugs like tirzepatide and semaglutide. This happens four times faster than after regular diet and exercise programmes.
Research shows 82% of patients gain back at least a quarter of their lost weight. Most people ended up at their starting weight within 1.5-1.7 years after stopping. Their blood pressure, cholesterol, and blood glucose also return to earlier levels within about 1.4 years.
What are the risks and side effects?
These powerful appetite-suppressing medications can cause side effects that need to be thought over carefully. Patients should understand both common reactions and potential risks to make informed treatment decisions.
Common side effects: nausea, fatigue, etc.
Gastrointestinal effects affect more than 1 in 10 patients. The most common ones include:
- Nausea (up to 22% of Mounjaro users experience this)
- Vomiting, diarrhoea and constipation
- Stomach pain and fatigue
- Headache and dizziness
Your body typically adjusts to these reactions within 4-8 weeks during dose escalation.
Rare but serious risks to watch for
Serious complications can occur, though they’re uncommon:
Severe abdominal pain might signal pancreatitis (pancreas inflammation). About 1 in 200 patients develop gallbladder problems, including gallstones. Severe dehydration can lead to kidney damage.
The MHRA has documented cases where patients needed hospital care due to severe dehydration after gastrointestinal reactions. Both medications come with a boxed warning about thyroid tumours found in animal studies.
How safe are the new weight loss drugs long-term?
Clinical evidence shows these medications are generally safe when properly monitored by medical professionals. The largest longitudinal study (STEP 5) lasted 2 years and showed the drug remained well-tolerated without new long-term risks.
The SURMOUNT trials monitored thousands of participants and produced consistently positive safety results. Notwithstanding that, safety monitoring continues as these medications become accessible to more people.
Conclusion
Mounjaro and Wegovy mark a breakthrough in treating obesity. This piece shows how these drugs work naturally with our body’s hormones to cut appetite and control weight. The results are impressive – tirzepatide’s dual-action mechanism works on both GLP-1 and GIP receptors. This explains why patients lose up to 20.9% of their weight compared to semaglutide’s 13.7%.
NHS availability stays limited right now. The rollout starts in June 2025 and will serve patients with the highest BMIs and multiple health issues first. Many patients who could benefit from these treatments must wait for later phases.
Without doubt, proper use of these medications brings remarkable results. Patients usually see changes in their appetite within weeks and lose substantial weight over several months. The biggest problem comes after stopping – most people go back to their original weight within two years.
Side effects need careful thought. Many users face stomach issues at first, but these usually get better as their body adapts. On top of that, rare but serious issues like pancreatitis and gallbladder problems need medical watching.
The outlook for 2026 and beyond suggests these treatments will become more available as healthcare systems adapt. New developments point to more advanced medications, including triple-action drugs that target multiple hormone pathways. This field grows faster each day.
Managing weight remains a tough health challenge. These innovative medications bring hope to millions who struggle with obesity and related health issues. Combining them with lifestyle changes and proper medical oversight gives patients the powerful tools they’ve waited for.
FAQs
Q1. What are the new weight loss drugs available on the NHS in 2026? As of 2026, the NHS offers two primary weight loss medications: Mounjaro (tirzepatide) and Wegovy (semaglutide). Mounjaro is a dual-action drug that targets both GLP-1 and GIP receptors, while Wegovy works solely on GLP-1 receptors.
Q2. Who is eligible for these new weight loss treatments on the NHS? Eligibility criteria are strict and based on BMI and comorbidities. For Mounjaro, patients initially need a BMI of at least 40 kg/m² with four specific weight-related health conditions. Wegovy has slightly different criteria, including a BMI of 35 or more (or 32.5+ for certain ethnic backgrounds) with at least one weight-related comorbidity.
Q3. How effective are these new weight loss medications? Clinical trials show impressive results. Mounjaro (tirzepatide) users lost an average of 20.2% body weight, while Wegovy (semaglutide) users lost 13.7% over the same period. Most patients begin to see visible weight loss between 4-8 weeks after starting treatment.
Q4. What are the common side effects of these weight loss drugs? The most common side effects include nausea, vomiting, diarrhoea, constipation, stomach pain, fatigue, headache, and dizziness. These typically occur during dose escalation and often improve within 4-8 weeks as the body adjusts to the medication.
Q5. What happens if you stop taking these weight loss medications? Upon discontinuation, weight regain is common. Studies indicate that 82% of patients regain at least a quarter of lost weight. Most people return to their baseline weight within 1.5-1.7 years of stopping treatment, with weight returning at approximately 0.8kg monthly.
