Semaglutide Results: What Clinical Trials Actually Show

You searched for semaglutide before and after. You want to know what people actually experience.

The most honest answer comes from the clinical trials, not from social media posts or testimonials. The STEP 1 trial (semaglutide) and SURMOUNT-1 trial (tirzepatide) are two of the largest weight management studies ever published in the New England Journal of Medicine. The SELECT trial added cardiovascular outcome data for semaglutide that changed how clinicians think about the broader health benefits.

This page covers what those trials actually showed, what the week-by-week experience typically looks like, and why individual results vary so significantly.

One important framing note before we start: all clinical trial data on this page reflects results from FDA-approved branded medications. Compounded formulations of semaglutide and tirzepatide are not FDA-approved products and have not been independently evaluated by the FDA for safety, efficacy, or quality. Clinical trial results for branded products cannot be assumed to apply to compounded versions.

For our full program overview, visit Compare GLP-1 Medications.

The STEP 1 trial: semaglutide outcomes

The STEP 1 trial was published in the New England Journal of Medicine in 2021. It was a randomized, double-blind, placebo-controlled trial conducted across multiple countries.

Who was in the trial

STEP 1 enrolled 1,961 adults with either obesity (BMI 30 or above) or overweight (BMI 27 or above) with at least one weight-related comorbidity. Critically, participants did not have type 2 diabetes. This is an important detail because semaglutide’s weight loss evidence in people without diabetes is what is most relevant to most people considering a GLP-1 program for weight management.

All participants received monthly counseling on diet and physical activity throughout the trial alongside either the medication or placebo. This is also important: the trial was not studying medication alone, but medication as part of a supported program.

What the trial found

Over 68 weeks, participants taking semaglutide 2.4mg weekly achieved:

• Mean body weight reduction: approximately 14.9% (roughly 15.3 kg or 33.7 lbs from baseline)
• 69.1% of participants lost 10% or more of body weight
• 50.5% of participants lost 15% or more
• 32.0% of participants lost 20% or more
• Significant improvements in waist circumference, blood pressure, blood sugar, and cholesterol markers

The placebo group, also receiving lifestyle counseling, lost approximately 2.4% of body weight over the same period. The difference in outcomes between the two groups reflects the medication’s effect above and beyond lifestyle support alone.

What the trial does not tell you

The 14.9% mean figure is a group average. Individual responses in the trial ranged widely. Some participants lost substantially more; some lost substantially less. The figure represents the midpoint of a distribution, not a prediction for any individual.

The trial also ended at 68 weeks. STEP extension studies tracked participants after discontinuation and showed significant weight regain following stopping the medication, which is discussed in more detail below.

The SURMOUNT-1 trial: tirzepatide outcomes

The SURMOUNT-1 trial was published in the New England Journal of Medicine in 2022. It followed a similar design to STEP 1 and was the pivotal trial that established tirzepatide’s weight management evidence base.

Who was in the trial

SURMOUNT-1 enrolled 2,539 adults with obesity or overweight with at least one comorbidity, without type 2 diabetes. Participants were randomized to three dose levels of tirzepatide (5mg, 10mg, or 15mg weekly) or placebo. All participants received lifestyle counseling.

What the trial found

Over 72 weeks, outcomes at the highest studied dose (15mg weekly) were:

• Mean body weight reduction: approximately 20.9% (roughly 22.5 kg or 49.6 lbs from baseline)
• 91% of participants achieved at least 5% weight loss
• 79% achieved at least 10% weight loss
• 57% achieved at least 20% weight loss

The lower dose groups produced lower mean outcomes: approximately 15.0% at 5mg and approximately 19.5% at 10mg. This matters because many patients do not reach the maximum studied dose due to tolerability. Your provider adjusts dose based on your response and side effect profile.

The placebo group lost approximately 3.1% of body weight over the same period.

The comparison to STEP 1

Tirzepatide’s SURMOUNT-1 results at the highest dose were higher than semaglutide’s STEP 1 results at its studied dose. This is the factual reading of the data.

What the direct comparison cannot tell you: these were different trials, different patient populations, different follow-up durations, and different dose titration protocols. There is no head-to-head trial of semaglutide vs tirzepatide at equivalent conditions in a single study. The SURMOUNT-5 trial (which compares them directly) is ongoing as of early 2026.

Both are substantial weight loss outcomes by any standard measure for clinical weight management. Which medication may be appropriate for your situation is a question for your provider.

The SELECT trial: cardiovascular outcomes

The SELECT trial (Semaglutide Effects on Heart Disease and Stroke in Patients with Overweight or Obesity) expanded the understanding of what GLP-1 medications can do beyond weight management.

Who was in the trial

SELECT enrolled approximately 17,600 adults with obesity or overweight, without type 2 diabetes, who had established cardiovascular disease (prior heart attack, stroke, or peripheral artery disease). It was a large, long-duration trial designed to assess cardiovascular outcomes rather than weight loss as a primary endpoint.

What the trial found

Over a median follow-up of approximately 33 months, participants taking semaglutide (FDA-approved branded version, 2.4mg weekly) experienced:

• A 20% reduction in major adverse cardiovascular events (MACE) compared to placebo. MACE was defined as cardiovascular death, non-fatal heart attack, or non-fatal stroke.
• This was a statistically significant finding at p less than 0.001.
• The results were published in the New England Journal of Medicine in 2023.

SELECT was the first large-scale trial to show a cardiovascular benefit for a GLP-1 medication in a population defined by obesity rather than type 2 diabetes. It shifted how clinicians think about GLP-1 medications from a weight loss tool to a broader cardiometabolic treatment.

What SELECT means for providers

For patients with a history of cardiovascular events and obesity, the SELECT data adds a layer to the clinical conversation beyond weight loss alone. Your provider weighs this evidence alongside your health history when determining whether a GLP-1 medication may be appropriate for your situation.

These results are for the branded medication studied in the trial. They cannot be assumed to apply to compounded formulations.

Week-by-week realistic expectations

The clinical trial outcomes take 68-72 weeks to fully develop. Understanding what the early weeks look like sets realistic expectations.

Weeks 1-4: dose adjustment

The standard titration for semaglutide starts at a low dose and increases gradually over several months before reaching the full therapeutic dose. During the first four weeks, you are at the starting dose, which is well below the doses that produced the trial outcomes.

Most people experience minimal appetite suppression during this phase. Some people notice mild nausea, reduced appetite, or GI symptoms as their body adjusts. The first month is not representative of what the medication will feel like at therapeutic doses.

Expecting significant weight loss in weeks 1-4 is not consistent with how titration works. What this period is for is establishing tolerability and giving your body time to adjust.

Weeks 4-12: more pronounced effects

As doses increase through the titration schedule, appetite suppression becomes more noticeable. Most people report a meaningful reduction in hunger and food preoccupation during this phase. Some describe a quieting of the persistent background thoughts about food that researchers have termed “food noise.”

Weight loss during this period is more consistent than in the first month. However, the rate of loss varies significantly by individual. Your starting weight, metabolic history, activity level, and how well you tolerate each dose increase all affect outcomes during this window.

Months 3-6: continued progress

By months 3-6, most people on a titration schedule have reached or are approaching the higher therapeutic doses studied in trials. This is typically the period of most sustained, consistent progress for people who tolerate the medication well.

Lifestyle habits established during this period matter for long-term outcomes. The clinical trials that produced the published results included lifestyle counseling alongside medication. The combination produces better outcomes than medication alone.

Months 6 and beyond

The trial data from STEP 1 and SURMOUNT-1 shows continued gradual progress through months 6-18 at therapeutic doses, with a slowing rate of loss as participants approach a new weight plateau. This is normal and expected. Weight loss does not continue linearly indefinitely.

This is also the phase where conversations with your provider about maintenance, dose adjustment, and long-term planning become relevant.

Why individual results vary significantly

Group averages from clinical trials describe the midpoint of a distribution. Understanding why individual responses vary helps set realistic expectations.

Starting weight

The percentage of body weight lost is a more consistent measure than absolute pounds, but absolute numbers matter for how progress feels. Someone starting at 220 lbs and losing 15% loses 33 lbs. Someone starting at 180 lbs and losing 15% loses 27 lbs. The percentage experience can be similar while the absolute numbers differ.

Metabolic health history

Years of weight cycling, prior calorie restriction, and metabolic adaptation all affect the rate at which the body responds. Someone with significant metabolic adaptation from repeated prior dieting may respond more slowly than someone early in their weight management history.

Dose achieved

The trial outcomes at the highest doses are higher than outcomes at lower doses. Not all patients reach the maximum studied dose. Some people have tolerability issues with higher doses and achieve their best outcomes at a moderate level. Your provider adjusts dosing based on your response rather than aiming for the highest dose at any cost.

Lifestyle factors

The clinical trials included lifestyle counseling alongside medication. Participants who made meaningful changes to eating patterns and activity during the trial experienced better outcomes than those who did not. GLP-1 medications reduce appetite signals, but they work within a larger context of how you eat and move.

Hormonal status

For perimenopausal women, hormonal changes affect how the body stores and loses fat. Estrogen decline shifts fat storage toward the abdomen and alters insulin sensitivity. Research from the SURMOUNT program and related analyses has shown meaningful weight loss outcomes in pre-, peri-, and postmenopausal women. Tirzepatide achieved approximately 20% weight reduction in women across menopausal status categories in SURMOUNT trial analyses. But hormonal context is part of the clinical picture your provider considers.

Duration of treatment

The 15% and 20% outcomes from STEP 1 and SURMOUNT-1 were achieved over 68-72 weeks. Shorter treatment courses produce lower outcomes. Discontinuing medication early also carries a higher risk of weight regain.

What happens when you stop

This is the question that deserves a direct answer.

A follow-up study from the STEP 1 trial program, published in Diabetes, Obesity and Metabolism (2022), tracked participants for one year after they stopped semaglutide. Participants regained approximately two-thirds of their lost weight within that year, and most metabolic improvements (blood pressure, blood sugar, cholesterol) also reversed toward baseline.

This is not a failure of the medication. It reflects the underlying biology of weight regulation: the hormonal drivers of appetite and fat storage that GLP-1 medications address do not permanently change when the medication is discontinued. When the medication stops, those drivers reassert themselves.

The most evidence-based approach to managing this is using the active treatment phase to build sustainable habits around eating, activity, and sleep. Those habits do not fully offset the biological rebound, but they substantially reduce it. Many people transition to a lower maintenance dose rather than stopping completely.

Your provider discusses this with you as part of the long-term plan. Transformation Health also offers a microdose maintenance program at a lower cost for patients who have reached their goal weight and want ongoing support.

What’s in this section

This sub-pillar covers specific results topics in more depth:

Tirzepatide Before and After SURMOUNT-1 and SURMOUNT-2 outcomes in detail, what the data shows for different dose levels, and how tirzepatide results have been interpreted in clinical practice.

How Much Weight Can You Lose on Semaglutide A detailed breakdown of STEP program outcomes, what factors predict higher vs lower response, and realistic ranges for different starting profiles.

Weight Loss Timeline: Week by Week A detailed walk-through of what titration schedules look like, what to expect at each phase, and what signs suggest the medication is working or not.

Semaglutide Before and After 1 Month What the first month on semaglutide typically looks like, why early results are limited, and what the first 30 days are actually for.

GLP-1 Clinical Trials: Landmark Study Results A reference guide to STEP 1, STEP 2, STEP 3, SURMOUNT-1, SURMOUNT-2, SELECT, and other major GLP-1 trials, with methodology, populations, and key findings.

For our full comparison of GLP-1 programs, see Compare GLP-1 Medications.