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Reading path6 guides, in order

I'm thinking about a GLP-1 for my weight. Where do I start?

A reading path for anyone weighing up Wegovy or Mounjaro, in the order that makes the decision easier.

GLP Guidebook teamUpdated 12 Oct 20265 min read17 sourcesWritten from published sources
The short answer

Start with your health, not the medicine. NICE uses BMI and waist-to-height to judge risk, with lower BMI thresholds for some ethnic groups. Medicines are one option, alongside food, activity and sometimes surgery. On the NHS, access is limited and differs between England, Scotland, Wales and Northern Ireland; most people who take them pay privately. GLP-1s are usually long-term and have side effects. These six guides walk you through the decision in order.

Read this page first. It covers what the BMI thresholds mean for you, who can get these medicines on the NHS, how to make the decision and what to expect if you start. At the end, six guides take you further, in order.
On this page
  1. BMI and waist thresholds
  2. Who can get it on the NHS
  3. The decision, step by step
  4. What to expect
  5. The risks, in brief
  6. What to read next
  7. Sources

What do the BMI thresholds mean for me?

They measure health risk. They don't decide whether you should take a medicine.

BMI (body mass index) compares your weight with your height. Waist size shows how much fat sits around your belly.

NICE, the body that writes guidance for the NHS in England, uses lower BMI thresholds for people from some ethnic backgrounds.1

BMIMost peopleSome ethnic groups*
Overweight25 to 29.9123 to 27.41
Obesity30 or more127.5 or more1

* People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background.1

Waist-to-height ratio. For anyone with a BMI under 35, NICE also uses your waist divided by your height. A ratio of 0.5 to 0.59 means increased belly fat, and 0.6 or more means high. For example, a 96.5 cm (38 in) waist and a height of 170 cm (5 ft 7 in) gives 0.57.1

Where medicines come in. Wegovy and Mounjaro are licensed in the UK for adults with a BMI of 30 or more, or 27 to under 30 with at least one weight-related health problem, such as high blood pressure.2,3 The licence has no separate ethnicity thresholds; NICE's lower thresholds are used for NHS eligibility.2,10

A number is not a prescription. Being over a threshold means a prescriber may consider a medicine. It doesn't mean you qualify. It's a starting point for a conversation with your GP or another prescriber.

Can I get it on the NHS?

Possibly, but the NHS rules are narrower than the licence, and they depend on where you live.

  • England, Mounjaro. GPs can prescribe it in stages. First, people with a BMI of 40 or more and at least 4 of these 5 conditions: high blood pressure, high blood fats (such as cholesterol), obstructive sleep apnoea, heart or blood-vessel disease, and type 2 diabetes. From around June 2026, a BMI of 35 to 39.9 with 4 of them. From around March 2027, a BMI of 40 or more with 3. The BMI lines are 2.5 lower for the ethnic groups in the table above.10 Some local NHS areas ask you not to contact your GP unless invited, and you must also take part in a support programme on food and activity.11
  • England, Wegovy. Only through a specialist weight management service, for up to 2 years.5 Since May 2026 there is a second route: people with established heart or blood-vessel disease and a BMI of 27 or more, to lower the risk of heart attack and stroke.12
  • Scotland. The Scottish Medicines Consortium accepted Mounjaro for restricted use in adults with a BMI of 30 or more and at least one weight-related condition, with a possibly lower BMI for minority ethnic groups.14 How quickly each health board offers it varies.
  • Wales. Mounjaro was given through specialist weight services, and since October 2025 also to some people waiting for time-sensitive surgery, a transplant or fertility treatment, or with conditions such as severe asthma or severe sleep apnoea.15
  • Northern Ireland. In April 2025, Mounjaro for obesity was not yet available on the Health Service, with a phased start planned over several years.16 Ask your GP for the current position.

Outside these routes, people pay privately. Guide 6 covers NHS and private prescriptions in detail.

How should I make the decision?

One step at a time, in this order. Each step has a guide.

1Check your numbers and health (Guide 1)
2Compare all your options (Guide 3)
3Ask if a GLP-1 fits you, and when not (Guide 4)
4Weigh the side effects (Guide 5)
5Talk to your GP; learn the NHS and private routes (Guide 6)
6Going private? Check the pharmacy or clinic first (Guide 7)
7Review how it's going at 6 months

Medicines don't replace food and activity changes. The WHO says GLP-1 treatment should come with support for healthy eating and physical activity.4

Step 6 matters if you go private. Since February 2025, the General Pharmaceutical Council (GPhC), which regulates pharmacies in Great Britain, has required online prescribers to check your weight, height or BMI themselves before prescribing a weight-loss medicine, rather than relying on an online form alone.13

The review step matters too. NICE says to consider stopping semaglutide (Wegovy) if you've lost less than 5% of your starting weight after 6 months.5 For tirzepatide (Mounjaro), if you've lost less than 5% after 6 months on the highest dose you can manage, it says to decide with your prescriber whether to carry on.10 For someone who started at 90 kg (14 st 2 lb), 5% is 4.5 kg (about 10 lb).

What should I expect if I do start?

Expect three things:

  • weight loss that is real, but varies a lot from person to person
  • stomach side effects for many people, especially early on
  • a long-term commitment, because the weight tends to return after stopping

The main semaglutide weight trial, STEP 1, shows what to expect. People were put into two groups at random. One group got the medicine and the other a dummy injection with no medicine in it. Both groups got the same diet and activity advice. So the gap between the two groups is what the medicine added.6

Average share of body weight lost, and what that means for someone who starts at 90 kg (14 st 2 lb):

STEP 1Semaglutide 2.4 mg (Wegovy), weekly

1,961 adults with obesity or overweight and no diabetes, 68 weeks.6

Semaglutide14.9%about 13 kg
Dummy injection2.4%about 2 kg

So about 12.5% of body weight, or 11 kg (1 st 11 lb) for a 90 kg person, came from the medicine itself.

These are averages, and people varied a lot. On semaglutide, about 86 in 100 lost at least 5% of their body weight, against about 32 in 100 on the dummy injection, and about 1 in 3 lost 20% or more. Put the other way, about 1 in 7 on semaglutide lost less than 5%.6

Most of the weight usually comes back after stopping. A year after stopping, people followed up from STEP 1 had regained about two-thirds of what they lost.7 So plan as if you'll stay on it. On the NHS in England, Wegovy is given for up to 2 years in specialist services; privately, you pay for every month.5 Guide 9 covers stopping.

Just a few pounds?It's for a family memberBMI calculator

What to read next, in order

These six guides go deeper. Each one ends with a link to the next, so you can read them one after another.

  1. 1Weight and health: what BMI and waist numbers meanGuide 1 of 9UnderstandCheck where you stand with BMI and waist-to-height, including NICE's lower thresholds for some ethnic groups.
  2. 2Your options, and where medicines fitGuide 3 of 9DecideSee lifestyle support, other medicines, GLP-1s and surgery side by side before you pick one.
  3. 3Should I consider a GLP-1? And when not toGuide 4 of 9DecideWho prescribers may consider for a GLP-1, and the times it isn't a good idea.
  4. 4Side effects and risksGuide 5 of 9DecideWhat the first weeks feel like, and the rarer risks to know before you start.
  5. 5Getting a prescription in the UKGuide 6 of 9Do it safelyNHS or private: who qualifies in each nation, who may prescribe, the brands, and fakes.
  6. 6Choosing a pharmacy, clinic or programmeGuide 7 of 9Do it safelyIf you go private: what online pharmacies, clinics and programmes offer, how they charge and what to check.
Was this page easy to understand?

Sources

  1. NICE. Overweight and obesity management. NICE guideline NG246, published 14 January 2025, updated 8 January 2026. Recommendations 1.9.10 and 1.9.11 (BMI classes and lower thresholds for named ethnic groups), and waist-to-height ratio. Link
  2. Novo Nordisk. Wegovy 2.4 mg FlexTouch, UK summary of product characteristics (SmPC), section 4.1. Electronic Medicines Compendium, revised September 2026. Link
  3. Eli Lilly. Mounjaro KwikPen, UK SmPC, section 4.1. Electronic Medicines Compendium, revised 29 August 2026. Link
  4. World Health Organization. WHO issues global guideline on the use of GLP-1 medicines in treating obesity. 1 December 2025. Link
  5. NICE. Semaglutide for managing overweight and obesity. Technology appraisal TA875, 8 March 2023. Recommendations 1.1 and 1.2 (specialist weight management services, maximum 2 years; consider stopping if less than 5% lost after 6 months). Declared interests: some invited clinical experts declare fees or grants from Novo Nordisk and Eli Lilly (NICE's own register of interests for this appraisal). Link
  6. Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM, 2021;384:989–1002. 1,961 adults without diabetes, 68 weeks. DOI
  7. Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022;24(8):1553–1564. 327 people followed for a year after stopping. DOI
  8. Novo Nordisk. Wegovy (semaglutide) US prescribing information, revised June 2026. Sections 1, 2.2, 5.2, 5.3, 5.5, 8.3, 17. (US label.) PDF
  9. Novo Nordisk. Ozempic (semaglutide) injection, US prescribing information and Medication Guide, revised May 2026. Sections 4, 5.3, 5.5, 5.6, 7.2, 8.5. (US label.) PDF
  10. NICE. Tirzepatide for managing overweight and obesity. Technology appraisal TA1026, 23 December 2024. Recommendations 1.1 and 1.2, section 4 (funding variation) and "What this means in practice" (phased groups and conditions). Link
  11. NHS South West London Integrated Care Board. Tirzepatide (Mounjaro) for weight management: patient information ("do not contact your GP practice or book appointments about tirzepatide medication unless invited"; wraparound care required). Updated 30 July 2026.
  12. NICE. Semaglutide for reducing the risk of major adverse cardiovascular events in people with cardiovascular disease and overweight or obesity. Technology appraisal TA1152, 7 May 2026. Link
  13. General Pharmaceutical Council. Online pharmacies to strengthen safeguards to prevent unsafe supply of medicines (guidance for pharmacies providing services at a distance, 4 February 2025). Link
  14. Scottish Medicines Consortium. Tirzepatide (Mounjaro) for obesity, SMC2653: accepted for restricted use. Link
  15. Welsh Government. People waiting for time-sensitive surgery to get weight-loss drugs on the NHS. 23 October 2025. Link
  16. Northern Ireland Formulary (Health and Social Care). Tirzepatide patient information leaflet ("Tirzepatide is not currently available through the Health Service in Northern Ireland for the treatment of obesity… It will be introduced as a phased approach, over a number of years"). April 2025.
  17. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know. GOV.UK, updated 5 February 2026. Link

Last checked 12 Oct 2026 · Next review due Jan 2027

How this page was made. Written by the GLP Guidebook team from the sources above: drug labels, published trials, NICE and international guidelines, and official NHS, MHRA and GPhC pages. It's general information, not medical advice. Talk to your GP or another qualified prescriber before starting, stopping or changing any medicine. How we write