How Fast Does Semaglutide Work? Trial Results by Week
Semaglutide weight-loss results come from fixed trial checkpoints: an average -10.6% at week 20, -14.9% at week 68, and a plateau near week 60. The 2.4 mg dose is reached at week 16, and appetite effects were measured at week 20, with lunch intake 35% lower than placebo.
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Semaglutide’s weight-loss results in trials are reported at fixed checkpoints, not week by week. In the STEP 4 trial, adults who reached the 2.4 mg weekly dose lost an average of 10.6% of their body weight during the first 20 weeks [6]. In STEP 1, the average loss was 14.9% at week 68, compared with 2.4% on placebo [2]. Weight loss continued until about week 60 before leveling off [2][9].
The first months are mostly about ramping up the dose. Wegovy injection starts at 0.25 mg once weekly for 4 weeks, then steps up every 4 weeks toward the maintenance dose [1]. In STEP 1, the schedule was 0.25, 0.5, 1.0 and 1.7 mg for 4 weeks each, with the 2.4 mg maintenance dose reached by week 16 [2][3]. The label allows a maximum of 7.2 mg weekly only after a patient has tolerated 2.4 mg for at least 4 weeks, and only when additional weight reduction is clinically indicated [1]. Wegovy tablets start at 1.5 mg once daily for 30 days and step up every 30 days through strengths of 1.5, 4, 9 and 25 mg [1]. In the oral trial (Study 7), escalation to 25 mg daily took 12 weeks, followed by 52 weeks of maintenance [1].
What changes first: appetite or the scale?
A 20-week trial in 72 adults with obesity compared semaglutide 2.4 mg weekly with placebo [3]. At week 20, energy intake at an unrestricted lunch was 35% lower with semaglutide (1736 versus 2676 kJ) [3]. Participants reported less hunger, more fullness and satiety, better control over eating, and fewer and weaker food cravings [3].
Body weight in that trial fell 9.9% with semaglutide versus 0.4% with placebo at week 20 [3]. The same trial found no evidence of delayed gastric emptying at week 20 when measured indirectly with paracetamol absorption [3].
What side effects happen while the dose climbs?
Nausea and diarrhea were the most common adverse events in STEP 1. They were mostly transient, mild to moderate, and subsided over time [2]. Gastrointestinal events led 4.5% of the semaglutide group to stop treatment, versus 0.8% of the placebo group [2].
In the 7.2 mg trials, nausea occurred in 39% of patients on 7.2 mg, 35% on 2.4 mg, and 13% on placebo; vomiting occurred in 22%, 16% and 6%, respectively [1]. Gastrointestinal problems led 3% of patients on 7.2 mg, 3% on 2.4 mg, and 0.3% on placebo to discontinue [1].
How much weight loss shows up by week 20?
STEP 4 was a randomized, double-blind withdrawal study run at 73 sites in 10 countries from June 2018 to March 2020 [6]. It enrolled 902 adults who all began semaglutide at week 0. After a 20-week run-in made up of 16 weeks of dose escalation and 4 weeks at the maintenance dose, 803 were randomized to continue the drug or switch to placebo [6][7]. During that run-in, the mean weight change was -10.6%, about -11.1 kg from a starting weight of 107.2 kg, among the 803 who were randomized [6].
That figure applies only to the people who reached the 2.4 mg dose by week 20 and were randomized. The label states that because patients who discontinued during titration or did not reach 2.4 mg were not eligible for the randomized period, the results may not reflect the experience of patients first starting Wegovy [1][7].
From week 20 to week 68, those who continued semaglutide lost another 7.9% on average, while those switched to placebo regained 6.9%, a difference of 14.8 percentage points [6][1].
Does losing under 5% by week 20 mean the drug has failed?
Not necessarily, based on group averages from a post hoc analysis of STEP 4. A responder was defined as someone who lost at least 5% of body weight by week 20; 88.0% of those randomized to semaglutide were responders [7].
From week 0 to week 68, responders lost an average of 19.7%. Non-responders who continued semaglutide lost an average of 6.4%, while non-responders switched to placebo lost 0.3% [7]. Overall, 86.2% of the semaglutide-randomized group reached at least 5% loss by week 68 [7].
Early response predicted later success in 96.4% of cases (positive predictive value), but early non-response predicted failure only 42.9% of the time (negative predictive value) [7]. For comparison, a post hoc analysis of the tirzepatide trial SURMOUNT-1 found that 18% of participants were below 5% loss at week 12, and 90% of that group reached 5% by week 72, taking an average of 24.8 weeks to get there [8].
What are the headline results at 64 to 72 weeks?
STEP 1 enrolled 1,961 adults with overweight or obesity and without diabetes for 68 weeks. Their mean starting weight was 105.3 kg and mean body mass index 37.9, and 74.1% were female [2]. Mean weight change was -14.9% with semaglutide versus -2.4% with placebo, equal to -15.3 kg versus -2.6 kg [2]. These are treatment-policy (intention-to-treat) estimates, meaning they count people who stopped the drug along the way [2].
In a trial of adults with type 2 diabetes, the average loss was 9.6%, compared with 14.9% in those without diabetes [9]. The 7.2 mg weekly dose produced an average loss of 18.7% at 72 weeks [5]. Oral semaglutide 25 mg daily produced an average loss of 13.6% at 64 weeks [5].
| Time point | Study and group | Average weight change |
|---|---|---|
| Week 20 | STEP 4 run-in, 803 adults who reached 2.4 mg [6] | -10.6% |
| Week 68 | STEP 1, adults without diabetes [2] | -14.9% |
| Week 68 | STEP 4, week-20 responders who continued [7] | -19.7% |
| Week 72 | 7.2 mg trial [5] | -18.7% |
| Week 104 | STEP 5, 304 adults [10] | -15.2% |
| Week 120 | STEP 1 extension, one year after stopping [13] | -5.6% net |
How much do individual results vary?
At week 68 in STEP 1, weight-loss thresholds of 5%, 10%, 15% and 20% were reached by 86.4%, 69.1%, 50.5% and 32.0% of the semaglutide group, versus 31.5%, 12.0%, 4.9% and 1.7% of the placebo group [2].
Across the STEP trials, 32% to 39.6% of participants lost more than 20% of their body weight, while 10.2% to 16.7% lost less than 5% [9]. Two predictors of lower response have been identified: type 2 diabetes, and male sex, with average losses of 8% to 9.3% in males versus 14% to 16.2% in females [9].
When does weight loss level off?
In STEP 1, the weight-loss phase did not reach its lowest point (nadir) until week 60 [2]. STEP 5 followed 304 adults for 104 weeks and found a mean change of -15.2% with semaglutide versus -2.6% with placebo; 77.1% versus 34.4% reached at least 5% loss, and 92.8% of participants completed the trial [10].
Weight and cardiometabolic measures plateaued after about 60 weeks and were sustained for a further year on treatment [9].
What support came with those trial numbers?
The label states that patients received instruction for a reduced-calorie diet of about a 500 kcal/day deficit and increased physical activity of at least 150 minutes per week, beginning with the first dose [1]. In STEP 1, participants had individual counseling sessions every 4 weeks and kept daily diet and activity diaries that were reviewed during those sessions [2].
A review of 42 phase 3 studies of obesity medications found that most used a 500 kcal/day calorie goal and at least 150 minutes per week of activity; 22 studies provided counseling at least monthly, and 16 more at least every 3 months [5].
Why are real-world results lower than trial numbers?
A Cleveland Clinic cohort study identified 7,881 adults who started injectable semaglutide or tirzepatide between 2021 and 2023, including 6,109 on semaglutide; 80.8% were on low maintenance doses [4]. Mean weight loss at 1 year was 8.7%. Those who stopped within 3 months lost 3.6%, those who stopped later lost 6.8%, and those who did not discontinue lost 11.9% [4]. The authors attribute the gap from trial results to higher rates of discontinuation and lower maintenance doses [4].
A study of two urban health systems in adults with BMI of 35 or higher found semaglutide was associated with 5.4% total weight loss at 1 year with any use, versus 7.2% among those with a full year of continuous orders [11]. Among adults with obesity and type 2 diabetes specifically, persistence with GLP-1 therapy often falls below 60% by 12 to 24 months, and adverse effects are the most cited reason for stopping [12].
What happens after stopping semaglutide?
The STEP 1 extension followed 327 people for a year after both the drug and the lifestyle program were stopped at week 68 [13]. The extension group came from sites in Canada, Germany and the UK, plus high-recruiting sites in the United States and Japan [13]. Their mean loss was 17.3% at week 68. By week 120 they had regained 11.6 percentage points, leaving a net loss of 5.6% below their starting weight [13].
At week 120, 48.2% were still at least 5% below baseline, and most cardiometabolic improvements had reverted toward baseline [13]. In round terms, about two-thirds of the prior weight loss was regained within one year of stopping [13][4].
Sources
- National Library of Medicine DailyMed. WEGOVY- semaglutide injection, solution; WEGOVY- semaglutide tablet.
- New England Journal of Medicine. Once-Weekly Semaglutide in Adults with Overweight or Obesity.
- Diabetes, Obesity and Metabolism. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. 2021.
- Obesity. Changes in weight and glycemic control following obesity treatment with semaglutide or tirzepatide by discontinuation status. 2025.
- Obesity Science & Practice. A Review of Lifestyle Interventions Provided as an Adjunct to Obesity Management Medications. 2026.
- JAMA. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial.
- PubMed Central. Clinically-Relevant Weight Loss is Achieved Independently of Early Weight Loss Response to Once-Weekly Subcutaneous Semaglutide 2.4 MG (STEP 4).
- PubMed Central. Weight reduction over time in tirzepatide-treated participants by early weight loss response: Post hoc analysis in SURMOUNT-1.
- PubMed Central. Semaglutide for weight loss: unanswered questions.
- Nature Medicine. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial.
- Obesity. Real-World Effectiveness of Semaglutide and Tirzepatide Compared With Bariatric Surgery. 2026.
- Current Diabetes Reports. Persistence in GLP-1-Based Therapy Among Adults with Obesity and Type 2 Diabetes: A Narrative Review of Definitions, Real-World Outcomes, and Determinants. August 15, 2026.
- PubMed Central. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension.
- eClinicalMedicine. Trajectory of weight regain after cessation of GLP-1 receptor agonists: a systematic review and nonlinear meta-regression.
Frequently asked questions
Does semaglutide work right away, in the first week?
Wegovy injection starts at 0.25 mg once weekly for the first 4 weeks before any step-up. The earliest measured appetite findings come from week 20 of a 72-person trial, where energy intake at a test lunch was 35% lower with semaglutide than placebo, with less hunger and fewer cravings. Weight-change figures are reported at measured points such as week 20 and week 68.
How much weight will I lose on semaglutide in a month?
The injection schedule starts at 0.25 mg weekly for 4 weeks and steps up every 4 weeks, reaching the 2.4 mg maintenance dose by week 16. The earliest widely cited checkpoint is week 20, where the STEP 4 run-in showed an average loss of 10.6% among the 803 adults who reached the 2.4 mg dose and were randomized. That is a group average, not a prediction for one person.
What are semaglutide results at 3 months?
Three months falls within dose escalation, which reaches the 2.4 mg dose by week 16. The nearest measured checkpoint is week 20: the STEP 4 run-in group that reached 2.4 mg had lost an average of 10.6% of starting weight. In a smaller 72-person trial, weight was down 9.9% versus 0.4% on placebo at week 20.
What are semaglutide results at 6 months?
The nearest reported milestones are week 20, with an average loss of 10.6% in the STEP 4 run-in group, and week 68, with an average loss of 14.9% in STEP 1. Between weeks 20 and 68, those who continued semaglutide lost a further 7.9% on average, while those switched to placebo regained 6.9%.
When does Wegovy reach its full dose?
For the injection, STEP 1 escalated through 0.25, 0.5, 1.0 and 1.7 mg for 4 weeks each, reaching the 2.4 mg maintenance dose by week 16. The label describes the same 4-week step schedule. The 7.2 mg maximum is reserved for patients who have tolerated 2.4 mg for at least 4 weeks. Dose decisions belong to the prescriber.
What if I have lost under 5% by week 20?
In a post hoc STEP 4 analysis, non-responders at week 20 who continued semaglutide lost an average of 6.4% from baseline by week 68, while those switched to placebo lost 0.3%. Early non-response predicted later failure only 42.9% of the time. These are group averages, and any decision about continuing belongs with a prescriber.
Why are real-world results lower than the trial numbers?
In a Cleveland Clinic cohort of 7,881 adults, average 1-year loss was 8.7%, and the authors point to higher discontinuation and lower maintenance doses than in trials. People who stopped within 3 months lost 3.6% on average, versus 11.9% for those who continued. Among adults with obesity and type 2 diabetes, persistence often drops below 60% by 12 to 24 months.
Is average weight loss smaller with type 2 diabetes?
On average, yes. A trial in adults with type 2 diabetes showed a mean loss of 9.6%, compared with 14.9% in those without diabetes. Type 2 diabetes is one of two identified predictors of lower total response, along with male sex, where average losses ran 8% to 9.3% versus 14% to 16.2% in females.
This article summarizes FDA labeling, published research and company information current as of September 14, 2026. It is not medical advice and does not replace a conversation with your own healthcare provider. How we research and verify.