Weekly semaglutide or tirzepatide injections, taken with changes to diet and activity, led to average weight loss of 15 to 21 percent in the main trials. Most weight returns if they are stopped. A doctor consultation is £195, and programmes with the medicine and monthly review start at £595 a month.
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Any of these needs to be seen the same day. If you are severely unwell, go to your nearest emergency department or call 999.
These medicines copy gut hormones that tell the brain you are full and slow the emptying of the stomach. Semaglutide acts on one hormone pathway and tirzepatide on two. Both are injected once a week, starting low and increasing every 4 weeks.NICE NG246, 2025
They are licensed for weight management with a body mass index of 30 or more, or 27 or more with a weight related condition such as high blood pressure or prediabetes. The thresholds are lower for people of South Asian, Chinese, Black African or Caribbean family origin.NICE NG246, 2025
In the STEP 1 trial, adults taking semaglutide lost an average of 14.9 percent of their weight over 68 weeks, against 2.4 percent with placebo. Around a third lost 20 percent or more.New England Journal of Medicine Wilding, 2021
In SURMOUNT 1, the highest dose of tirzepatide gave an average loss of 20.9 percent over 72 weeks. The lowest dose gave 15 percent, which is why the dose is matched to response rather than pushed to the top.New England Journal of Medicine Jastreboff, 2022
In people with heart disease and overweight but no diabetes, semaglutide reduced heart attacks, strokes and cardiovascular deaths by a fifth over about three years.New England Journal of Medicine Lincoff, 2023
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The first consultation measures weight, height, waist and blood pressure, and goes through your history, medicines and previous attempts. It also screens for an eating disorder, pancreatitis and a personal or family history of thyroid cancer of the medullary type, each of which rules the medicines out.NICE NG246, 2025
Bloods at the start include HbA1c, kidney and liver function and cholesterol. They set the baseline the programme is measured against, and sometimes find prediabetes or diabetes that changes the treatment.NICE TA875, 2023
Contraception is agreed before the first dose, because these medicines must not be taken in pregnancy and should be stopped at least 2 months before trying to conceive.NICE TA1026, 2024
Diet and activity on their own
The base of every plan. A structured programme typically gives a loss of around 5 percent, which is enough to improve blood pressure and blood sugar.NICE NG246, 2025
Medicine through a specialist weight service
Offered to people who meet stricter criteria set by NICE, with semaglutide limited to two years of use.NICE TA875, 2023
Semaglutide
A weekly injection with the longest safety record and proven heart benefit in people with heart disease.New England Journal of Medicine Lincoff, 2023
Tirzepatide
A weekly injection giving greater average weight loss in trials, with similar stomach side effects.New England Journal of Medicine Jastreboff, 2022
Surgery
Gastric bypass or sleeve gastrectomy gives the largest and most lasting loss, for people with a high body mass index. We refer for it rather than perform it.NICE NG246, 2025
Weight usually comes back when the medicine stops. A year after stopping semaglutide in the STEP 1 extension, people had regained about two thirds of the weight they lost. These are long term medicines, and the plan for coming off is agreed at the start.Diabetes Wilding, 2022
Nausea, diarrhoea, constipation and reflux affect most people at some point, mainly in the first weeks and after each dose increase. They settle for most, and going up in dose more slowly helps. A small number stop because of them.New England Journal of Medicine Wilding, 2021
Part of the weight lost is muscle. Enough protein and resistance exercise two or three times a week reduce the share that is muscle, which matters more with age.UK Chief Medical Officers CMO report, 2019
Work out your body mass index. Divide your weight in kilograms by your height in metres, then divide by your height again. A result of 30 or more, or 27 or more with high blood pressure, prediabetes or sleep apnoea, is the usual starting point.NICE NG246, 2025
Measure your waist halfway between the lowest rib and the top of the hip bone. A waist more than half your height points to raised risk even when the body mass index looks acceptable.NICE NG246, 2025
Do not buy weight loss injections online without a consultation, or from a salon or social media seller. Fake pens are in circulation, and a prescriber who never checks your history cannot tell you when the medicine is unsafe for you.
Do not start on the highest dose to lose weight faster. It does not save time, it raises the chance of side effects that make people stop, and many people reach their goal on a middle dose.New England Journal of Medicine Jastreboff, 2022
Step 1
A 30 minute consultation with measurements, history and the reasons these medicines might not suit you. Bloods where they are needed.
Step 2
The first pen delivered with instructions. The dose increases every 4 weeks, and only when the side effects allow.
Step 3
Weight, side effects, protein and exercise each month, with bloods repeated at six months. The long term plan is written down, including how to come off.
Ask before you book if you are not sure this is the right appointment.
In the main trials, the average was about 15 percent of body weight with semaglutide and up to 21 percent with tirzepatide, over around a year and a half. Averages hide a wide range. Some people lose far more, and a few lose very little.
A doctor consultation is £195. Programmes including the medicine, a monthly doctor call and bloods start at £595 a month. The £945 a month programme adds monthly video review and a nutritionist, and the £2,150 programme adds a strength coach.
Usually with a body mass index of 30 or more, or 27 or more with a condition linked to weight, such as high blood pressure, prediabetes or sleep apnoea. The thresholds are lower for some ethnic groups. A doctor also checks for anything in your history that makes the medicines unsafe.
Appetite returns and most people regain much of the weight within a year. For that reason the medicines are treated as long term, and stopping is planned rather than sudden, with the diet, exercise and strength work built up first so they carry on without the medicine.
Nausea, diarrhoea, constipation, reflux and tiredness are common, mostly early on and after dose increases. Less common but serious are pancreatitis and gallstones. Severe abdominal pain means stopping the medicine and being seen the same day.
Not while trying to conceive or pregnant. The medicine should be stopped at least 2 months before trying. Tirzepatide can make the contraceptive pill less reliable, so the doctor goes through contraception before the first dose and after each increase.
Tirzepatide gives greater average weight loss in trials. Semaglutide has proven heart benefit in people with heart disease and a longer safety record. The choice depends on your goals, your history and how you tolerate the first weeks, and it can be changed.
This page is general information about a condition and it is not a diagnosis. Treatment depends on what a doctor finds when they examine you, and no outcome is guaranteed. If you are severely unwell, or if any of the warnings at the top of this page apply to you, go to your nearest emergency department or call 999.
Diabetes, Obesity and Metabolism
Weight regain and cardiometabolic effects after withdrawal of semaglutide, the STEP 1 trial extensionWilding, 2022
New England Journal of Medicine
Once weekly semaglutide in adults with overweight or obesity, STEP 1Wilding, 2021
New England Journal of Medicine
Tirzepatide once weekly for the treatment of obesity, SURMOUNT 1Jastreboff, 2022
New England Journal of Medicine
Semaglutide and cardiovascular outcomes in obesity without diabetes, SELECTLincoff, 2023
NICE
NICE
Tirzepatide for managing overweight and obesityTA1026, 2024
NICE
Overweight and obesity managementNG246, 2025
UK Chief Medical Officers
Physical activity guidelines, UK Chief Medical Officers reportCMO report, 2019
Written and reviewed by the clinical team at The Wellness. Last reviewed 23 September 2026.
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