Wegovy Results: What the STEP Trials Show

In the STEP trials, adults taking Wegovy (semaglutide 2.4mg) alongside diet and activity support lost on average around 15% of their body weight over about 16 months, compared with around 2 to 3% on placebo. About half of participants in STEP 1 lost at least 15%, though some lost much less. People with type 2 diabetes lost less on average, at about 10%. The newer 7.2mg dose produced average weight loss of about 19% in the STEP UP trial. Most of the weight loss happens in the first year, then levels off, and most people regain weight if they stop. This guide sets out what each trial found and what the numbers mean in practice.

The STEP trial programme at a glance

The STEP (Semaglutide Treatment Effect in People with obesity) programme is a series of randomised controlled trials that formed the basis for Wegovy's licence. All participants received lifestyle advice alongside either semaglutide or placebo.

These are average figures from the trials' main analyses. For an overview of the medicine, see the Wegovy hub and our complete UK guide.

STEP 1: the key trial

Design

STEP 1 enrolled 1,961 adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition, who did not have diabetes. Participants were randomised two to one to weekly semaglutide 2.4mg or placebo for 68 weeks. Everyone received lifestyle counselling, including a reduced-calorie diet and increased physical activity.

Average weight loss

The average change in body weight was -14.9% with semaglutide versus -2.4% with placebo, a difference of about 12.4 percentage points.

How many people reached key thresholds

Source: STEP 1, New England Journal of Medicine, 2021.

These thresholds matter because a 5% to 10% weight loss is associated with meaningful improvements in blood pressure, blood sugar and other health markers. Larger losses are associated with greater improvements in conditions such as sleep apnoea and joint pain.

Other outcomes

STEP 1 also found improvements in waist circumference, blood pressure, blood sugar markers, blood fats and physical functioning scores. About 4.5% of people on semaglutide stopped treatment because of gastrointestinal side effects, compared with 0.8% on placebo. See Wegovy side effects.

A month-by-month picture

The trials report average results, but it helps to understand the general shape of weight loss over time. The table below describes the typical pattern seen in STEP 1. It is a general guide, not a prediction for any individual.

In STEP 1, average weight loss began to plateau at around week 60. STEP 5 showed that, on average, weight loss was maintained to two years in people who continued treatment.

Our guide to realistic weight loss expectations explores the range of experiences, and weight loss plateaus explains why a plateau is expected.

People with type 2 diabetes: STEP 2

STEP 2 enrolled adults with overweight or obesity and type 2 diabetes. Average weight loss over 68 weeks was about 9.6% on semaglutide 2.4mg and about 3.4% on placebo. A 1mg semaglutide arm lost less than the 2.4mg arm.

People with type 2 diabetes tend to lose less weight on GLP-1 medicines than people without diabetes. The reasons are not fully understood but may include effects of other diabetes medicines, such as insulin, and differences in metabolism. Improvements in blood sugar control are an important benefit in this group. See GLP-1 medication and type 2 diabetes.

With intensive lifestyle support: STEP 3

STEP 3 combined semaglutide with intensive behavioural therapy, including an initial eight-week low-calorie meal replacement diet and frequent counselling sessions. Average weight loss was about 16.0% on semaglutide and about 5.7% on placebo. The extra support improved placebo results more than semaglutide results, suggesting the medicine accounts for most of the difference.

Maintaining weight loss: STEP 4 and STEP 5

STEP 4

In STEP 4, all participants took semaglutide for 20 weeks, reaching 2.4mg, and lost on average about 10.6%. They were then randomised to continue semaglutide or switch to placebo for a further 48 weeks. Those who continued lost a further 7.9% on average, while those who switched to placebo regained 6.9%.

STEP 5

STEP 5 followed adults without diabetes for two years. Average weight loss was about 15.2% on semaglutide versus about 2.6% on placebo at 104 weeks, showing that weight loss was largely maintained with continued treatment.

What happens after stopping: the STEP 1 extension

After STEP 1 ended, a subset of participants was followed for a further year without treatment. On average, people who had taken semaglutide regained about two-thirds of the weight they had lost. Improvements in blood pressure, blood sugar and other markers also moved back towards their starting levels.

This is consistent with the view, reflected in NICE guidance and the wider medical literature, that obesity is a chronic condition and that the effects of GLP-1 medicines depend on ongoing treatment. See Wegovy maintenance and stopping, weight regain after stopping and obesity as a chronic disease.

The 7.2mg dose: STEP UP

STEP UP enrolled 1,407 adults with obesity without diabetes, randomised to semaglutide 7.2mg, semaglutide 2.4mg or placebo for 72 weeks. Average weight loss was about 18.7% on 7.2mg, compared with about 3.9% on placebo, and the 7.2mg group lost more than the 2.4mg group. Nearly one in three people on 7.2mg lost at least 25% of their body weight. Gastrointestinal side effects and dysaesthesia (altered skin sensation) were more frequent on 7.2mg.

The MHRA approved the 7.2mg dose for adults with obesity in January 2026. NICE had not assessed it for NHS use at the time of writing. See Wegovy doses explained.

Other STEP trials worth knowing

STEP 8: semaglutide versus liraglutide

STEP 8, published in JAMA in 2022, compared weekly semaglutide 2.4mg directly with daily liraglutide 3mg (the active ingredient in Saxenda) in adults with obesity or overweight without diabetes. Over 68 weeks, average weight loss was about 16% with semaglutide and about 6% with liraglutide. More people stopped liraglutide early. This trial helps explain why semaglutide has largely replaced liraglutide in UK practice. See Saxenda vs newer GLP-1 medications.

STEP TEENS: adolescents

STEP TEENS, published in the New England Journal of Medicine in 2022, studied semaglutide 2.4mg in adolescents aged 12 to under 18 with obesity. Over 68 weeks, average BMI fell by about 16% on semaglutide, compared with a small increase on placebo. This trial supported the licence for adolescents aged 12 and over, under specialist care.

STEP HFpEF: heart failure

STEP HFpEF, published in the New England Journal of Medicine in 2023, studied people with obesity and heart failure with preserved ejection fraction. Semaglutide 2.4mg led to greater improvements in heart failure symptoms, physical limitations and exercise capacity than placebo, as well as greater weight loss.

Body composition: what kind of weight is lost?

Any significant weight loss includes some lean mass, which includes muscle, as well as fat. A body-composition substudy of STEP 1 using DXA scans found that the majority of the weight lost was fat, with a reduction in lean mass that was smaller in absolute terms. Because fat fell more than lean mass, the proportion of lean mass in the body increased.

Lean mass is not the same as muscle, and measurement methods have limitations. Even so, preserving muscle is a sensible goal. Eating enough protein and doing regular resistance exercise are widely recommended. See preserving muscle on GLP-1 treatment and protein on GLP-1 treatment.

What these results mean for health

Weight loss of 5% to 10% is associated with improvements in blood pressure, blood sugar, blood fats and the risk of developing type 2 diabetes. Larger amounts of weight loss, of 15% or more, are associated with improvements in conditions such as obstructive sleep apnoea, knee osteoarthritis symptoms and fatty liver disease.

The STEP trials were designed mainly to measure weight change and related risk factors. The SELECT trial adds direct evidence that semaglutide 2.4mg reduces cardiovascular events in people with established heart disease. For many people, these health benefits matter more than the number on the scales.

Questions to ask your prescriber about results

1. What would a good response look like for me, given my health conditions?
2. How will you measure progress, beyond body weight?
3. What happens if I lose less than 5% after six months?
4. Would the 7.2mg dose be appropriate for me later on?
5. What is the plan for maintaining weight loss in the long term?

Beyond the scales: health outcomes

Cardiovascular events: SELECT

SELECT enrolled more than 17,000 adults with established cardiovascular disease and a BMI of 27 or more, without diabetes. Semaglutide 2.4mg reduced the risk of major adverse cardiovascular events by 20% compared with placebo. Average weight loss in SELECT was smaller than in STEP 1, at around 10%, and the cardiovascular benefit appeared to begin early, which suggests effects beyond weight loss. See Wegovy and heart health.

Other measures

The STEP trials also reported improvements in:

• Waist circumference, a marker of abdominal fat.
• Blood pressure.
• Blood sugar markers such as HbA1c.
• Blood fats.
• Physical function and quality of life scores.

See measuring progress beyond the scales.

Wegovy compared with other medicines

These figures come from separate trials with different populations, except STEP 8 and SURMOUNT-5, which compared medicines directly. In SURMOUNT-5, tirzepatide produced about 20% average weight loss versus about 14% for semaglutide 2.4mg over 72 weeks. See Mounjaro results, Mounjaro vs Wegovy and SURMOUNT-5 explained.

How to read trial results

Averages hide a wide range

An average of 15% includes people who lost 30% or more and people who lost less than 5%. Around one in seven people in STEP 1 did not reach 5% weight loss.

Two ways of measuring

Trials often report two types of result. The "treatment policy" estimand includes everyone randomised, whether or not they kept taking the medicine. The "trial product" estimand estimates the effect in people who took the medicine as intended, and usually shows larger numbers. Headline figures can differ depending on which is reported. The figures in this guide are mainly from the trials' primary analyses.

Trial conditions differ from everyday life

Trial participants receive regular visits, lifestyle counselling and close monitoring. Results in everyday practice may differ, either because support is less intensive or because people stop treatment sooner.

Factors that affect individual results

• Diabetes status: people with type 2 diabetes tend to lose less.
• Dose tolerated: people who cannot reach 2.4mg may lose less.
• Adherence: missing doses or stopping early reduces results.
• Diet and activity: the medicine is licensed for use alongside lifestyle changes.
• Other medicines: some medicines, such as certain antidepressants, steroids or insulin, can make weight loss harder.
• Biology: genetics and individual physiology play a role, and there are no reliable tests to predict response.

If you are not losing weight as expected, speak to your prescriber. See what if GLP-1 treatment doesn't work for you.

Accessing treatment

On the NHS, Wegovy is available within specialist weight management services under NICE TA875, for up to two years. Privately, regulated providers can prescribe it after a consultation. See Wegovy on the NHS. To compare how regulated services handle consultations and follow-up, see our provider comparison; for what affects cost, see our prices page.

When to speak to a professional

Speak to your GP, pharmacist or a regulated prescriber if you are considering Wegovy, so they can assess whether it is suitable for you and discuss realistic expectations.

During treatment, contact your prescriber if:

• You have lost less than 5% of your body weight after six months on treatment.
• You are losing weight very quickly or struggling to eat enough.
• Side effects are preventing you from reaching the maintenance dose.
• You are thinking about stopping treatment.
• You notice changes in mood or your relationship with food.

Seek urgent medical help (NHS 111, or 999 / A&E in an emergency) if you have:

• Severe, persistent abdominal pain, which may spread to your back, with or without vomiting.
• Pain in the upper right abdomen, fever or yellowing of the skin or eyes.
• Signs of severe dehydration, such as confusion or passing very little urine.
• Signs of a serious allergic reaction, such as swelling of the face or throat, or difficulty breathing.

Results vary from person to person, and decisions about continuing, adjusting or stopping treatment belong to your prescriber.