Semaglutide gives its first clear results after a few months, and the full result after more than a year. In the STEP 4 trial, participants lost an average of 10.6 percent of their body weight in the first 20 weeks. After 68 weeks in the STEP 1 trial the loss was 14.9 percent, or 15.3 kg. If you want to know what to expect after a month, after half a year and after two years, below you will find the figures from successive trials of the STEP programme.
Why does the first month of semaglutide give little?
The first month serves to introduce the dose, not to lose weight. The US label of Wegovy starts with 0.25 mg once a week for four weeks. After that the dose rises every four weeks: to 0.5 mg, 1 mg and 1.7 mg. The target 2.4 mg is taken only from week 17.
| Weeks | Weekly dose |
|---|---|
| 1-4 | 0.25 mg |
| 5-8 | 0.5 mg |
| 9-12 | 1 mg |
| 13-16 | 1.7 mg |
| from week 17 | 2.4 mg |
The starting dose is therefore almost ten times smaller than the target dose. Its job is to get the digestive tract used to semaglutide. The published trials do not report the average weight loss after the first four weeks separately.
How many kilograms go in the first 20 weeks?
After 20 weeks the average weight loss was 10.6 percent. This is the result of the STEP 4 trial, published in 2021 in JAMA. All participants first went through 16 weeks of dose escalation and 4 weeks at 2.4 mg. This part of the trial enrolled 902 adults with obesity or overweight.
The 10.6 percent figure refers to the 803 people who reached the 2.4 mg dose. They made up 89.0 percent of everyone who started. At a weight of 100 kg, such a loss would mean about 10.6 kg in under five months. This is the earliest point at which the STEP programme reports an average result.
What does the full STEP 1 trial show after 68 weeks?
After 68 weeks body weight fell by an average of 14.9 percent on semaglutide and 2.4 percent on placebo. STEP 1 appeared in 2021 in the New England Journal of Medicine. It included 1961 adults with obesity, or overweight with a related condition, without diabetes. Both groups also received lifestyle support.
| Result after 68 weeks | Semaglutide 2.4 mg | Placebo |
|---|---|---|
| Average weight loss | 14.9 percent (15.3 kg) | 2.4 percent (2.6 kg) |
| Loss of at least 5 percent | 86.4 percent of people | 31.5 percent of people |
| Loss of at least 10 percent | 69.1 percent of people | 12.0 percent of people |
| Loss of at least 15 percent | 50.5 percent of people | 4.9 percent of people |
Half of the people on semaglutide lost at least 15 percent of their body weight. The results include all participants, also those who stopped treatment or turned to other methods. Cardiovascular risk factors and physical functioning reported by the participants themselves also improved.
Does weight keep falling after 20 weeks?
Yes, with continued use body weight kept falling for another 48 weeks. In STEP 4, people who continued semaglutide lost an additional 7.9 percent from week 20 to week 68. Their waist circumference shrank by 9.7 cm more than in the comparison group over that time. Systolic blood pressure also fell.
The group switched to placebo after 20 weeks gained 6.9 percent over the same period. The difference between the groups was 14.8 percentage points. The authors conclude that staying on semaglutide brings further weight loss, and stopping it reverses that.
What does the result look like after two years?
After 104 weeks weight loss was 15.2 percent versus 2.6 percent on placebo. This is the result of the STEP 5 trial, published in 2022 in Nature Medicine. It included 304 adults with an average weight of 106.0 kg. After two years, 77.1 percent of people on semaglutide had lost at least 5 percent of their weight.
Comparing STEP 1 and STEP 5 shows how the effect spreads over time. Most of the loss appears in the first fifteen or so months. In the second year body weight mainly stays at the lower level.
How is the effect spread over the months?
Body weight falls fastest in the first five months, after which the pace slows clearly. A comparison of three STEP trials shows this in figures. Each of them measured the loss from the same starting point.
| Time from start | Average weight loss | Trial |
|---|---|---|
| 20 weeks (about 5 months) | 10.6 percent | STEP 4 |
| 68 weeks (about 16 months) | 14.9 percent | STEP 1 |
| 104 weeks (2 years) | 15.2 percent | STEP 5 |
The figures come from different groups of people, so they show a direction, not the exact curve of one person. A model published in 2023 in Diabetes, Obesity and Metabolism confirms this picture. According to its authors, the course of weight loss follows how much semaglutide circulates in the blood in successive weeks.
Does semaglutide work more slowly than tirzepatide?
In real-world data, semaglutide gave a somewhat slower weight loss than tirzepatide. A 2026 analysis of medical records compared 10,339 people on each of them. Semaglutide gave an average weight loss of 2.18 percent per month, tirzepatide 2.54 percent. A loss of at least 15 percent in the first year was reached by 21.6 percent of people on semaglutide.
A direct comparison of both molecules is in the guide semaglutide vs tirzepatide vs retatrutide. The effects of semaglutide beyond body weight, including on the heart and kidneys, are covered in the guide on semaglutide and tirzepatide for the heart, kidneys, sleep and liver.
Which side effects appear at the start?
The most common were nausea and diarrhoea, usually transient and mild or moderate. The STEP 1 authors write that they eased over time. Because of gastrointestinal symptoms, 4.5 percent of people on semaglutide and 0.8 percent on placebo stopped treatment. In STEP 5 such symptoms were reported by 82.2 percent of people on semaglutide versus 53.9 percent on placebo.
That is exactly why the dose is raised gradually over 16 weeks. A slower pace of dose increases gives the digestive tract time to adapt to semaglutide.
How much does semaglutide cost in the shop?
The shop has semaglutide 3 mg Bio-Peptide for 90 EUR. The vial contains a lyophilised powder that has to be dissolved before use. How many weeks one vial lasts at successive doses is calculated in the guide on how long a GLP-1 vial lasts.
A description of the molecule and current availability are on the semaglutide page. How semaglutide in a vial differs from the medicine is explained in the guide on why semaglutide and tirzepatide are prescription-only. The product in the shop is material for laboratory research, not the medicine Wegovy or Ozempic.
Frequently asked questions
When do the first effects of semaglutide show?
In the STEP 4 trial the average weight loss after 20 weeks was 10.6 percent. The first four weeks are the 0.25 mg starting dose, which serves to introduce treatment.
How many kilograms can you lose on semaglutide in a year?
In STEP 1 the average loss after 68 weeks was 14.9 percent, or 15.3 kg. Half of the participants lost at least 15 percent of their body weight.
When does semaglutide work at the full dose?
According to the Wegovy label, the 2.4 mg dose is taken from week 17. Before that the dose rises every four weeks from 0.25 mg.
Does semaglutide still work after two years?
In the STEP 5 trial, weight loss after 104 weeks was 15.2 percent versus 2.6 percent on placebo.
What happens after stopping semaglutide?
In STEP 4, people switched to placebo after 20 weeks gained 6.9 percent of their body weight within 48 weeks. People who continued semaglutide lost an additional 7.9 percent over that time.
Sources
- Wilding JPH, Batterham RL, Calanna S et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 2021, 384(11): 989-1002. https://doi.org/10.1056/NEJMoa2032183
- Rubino D, Abrahamsson N, Davies M et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance in Adults With Overweight or Obesity: The STEP 4 Randomized Clinical Trial. JAMA, 2021, 325(14): 1414-1425. https://doi.org/10.1001/jama.2021.3224
- Garvey WT, Batterham RL, Bhatta M et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nature Medicine, 2022, 28(10): 2083-2091. https://doi.org/10.1038/s41591-022-02026-4
- Strathe A, Horn DB, Larsen MS et al. A model-based approach to predict individual weight loss with semaglutide in people with overweight or obesity. Diabetes, Obesity and Metabolism, 2023, 25(11): 3171-3180. https://doi.org/10.1111/dom.15211
- Venkatakrishnan AJ, Murugadoss K, Soundararajan V. Weight-loss dynamics with tirzepatide versus semaglutide. PNAS Nexus, 2026, 5(6): pgag171. https://doi.org/10.1093/pnasnexus/pgag171
- Novo Nordisk. WEGOVY (semaglutide) injection, prescribing information, DailyMed, version of June 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b