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Trial results

How long does Ozempic or Zepbound take to work? What the trials found

Appetite often changes within weeks, but the scale moves more slowly. Here is what the trials measured at week 8, 20, 36 and beyond, what the labels say about dose steps, and how long the medicine stays in your body.

By 7 min read
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The short version
  • Weight starts to come down in the first weeks, but the full effect takes more than a year: in the semaglutide 2.4 mg trials, weight kept falling until about week 60.10
  • By week 20, adults on semaglutide (Wegovy) had lost 10.6% of their weight on average in STEP 4. By week 36, adults on tirzepatide (Zepbound) had lost 20.9% in SURMOUNT-4.7,9
  • Semaglutide has a half-life of about 1 week and tirzepatide about 5 days. The Wegovy label says semaglutide stays in the circulation for 5 to 7 weeks after the last dose.1,2

Why it takes longer than people expect

Semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) are not started at full strength. Both labels begin with a low dose and step it up every four weeks, mainly to reduce stomach side effects.1,2 So for the first few months, most people are not yet on the dose that was tested for weight loss.

The medicine also builds up in the body. The Ozempic label says steady levels of semaglutide are reached after 4 to 5 weeks of weekly doses, and the Zepbound label says tirzepatide reaches steady levels after 4 weeks.2,3

The schedules below are what the FDA labels describe. They are not advice. Your prescriber sets your own doses and timing.

MedicineLabel's starting doseStepsReaches maintenance
Wegovy injection (weekly)0.25 mg, weeks 1–40.5 mg, 1 mg, 1.7 mg, each for 4 weeksWeek 17 onward (2.4 mg recommended for weight reduction)
Wegovy tablets (daily)1.5 mg, days 1–304 mg, then 9 mg, each for 30 daysDay 91 onward (25 mg)
Zepbound injection (weekly)2.5 mg for 4 weeks5 mg, then up in 2.5 mg steps after at least 4 weeks each5, 10 or 15 mg maintenance
 Dose-escalation schedules as written in the FDA labels. Source: Wegovy and Zepbound prescribing information.1,2

The Zepbound label is explicit that the 2.5 mg starting dose "is for treatment initiation" and is not approved as a maintenance dose.2

Illustration of a row of calendar pages along a path.

How long does it take to start working?

Appetite changes come first. In small, tightly controlled studies, people were offered as much food as they wanted and researchers measured how much they ate.

  • After 12 weeks of semaglutide (stepped up to 1.0 mg) in 30 adults with obesity, total intake across a day of free meals was 24% lower than on placebo, and weight was down 5.0 kg from baseline.5
  • After 20 weeks of semaglutide 2.4 mg in 72 adults with obesity, intake at a free lunch was 35% lower than on placebo, and weight was down 9.9%.6
  • In adults with type 2 diabetes, people assigned to tirzepatide 15 mg already cut lunch intake by 185 kcal more than placebo at week 8.14

How long does Ozempic take to work for weight loss?

Ozempic is approved for type 2 diabetes. The weight-loss trials used semaglutide at the 2.4 mg Wegovy dose, in adults without diabetes. No single paper reports every week, so the table pulls time points from several trials. Each row names its source.

Time on treatmentWhat was measuredTrial
Week 862.1% on tirzepatide had lost at least 5%SURMOUNT-1 analysis4
Week 20−10.6% average on semaglutide 2.4 mgSTEP 4 run-in7
Week 2444% on tirzepatide and 21% on semaglutide had lost at least 15%SURMOUNT-5 analysis8
Week 36−20.9% average on tirzepatide 10 or 15 mgSURMOUNT-4 lead-in9
About week 60Weight loss on semaglutide levels offSTEP 1 and STEP 2, per STEP 5 authors10
Week 68−14.9% average on semaglutide 2.4 mg (−2.4% placebo)STEP 111
Week 72−15.0% to −20.9% on tirzepatide 5–15 mg (−3.1% placebo)SURMOUNT-112
 Time points from different trials with different populations and methods, so rows are not directly comparable. The STEP 4 and SURMOUNT-4 numbers are for people who completed the open-label start of those trials.

The pattern is the same in both drug programs: steady loss during the first year, then a slower phase and a plateau. For what happens after that point, see our article on the GLP-1 weight loss plateau.

Does early weight loss predict the final result?

Somewhat, but slow starters still do well. A 2026 analysis of SURMOUNT-1 split tirzepatide users by whether they had lost at least 5% by week 8, when everyone had been on 5 mg for four weeks.4

−23.3%at week 72 for early responders (lost ≥5% by week 8)
−14.6%at week 72 for everyone else

At week 8 the two groups had lost 7.9% and 3.1%. By week 72, 91.7% of early responders and 69.1% of the others had lost at least 10%.4 This was a post hoc analysis of people who stayed on treatment, and several authors work for the drug's maker.

In SURMOUNT-5, which compared the two medicines head to head, 44% of people on tirzepatide and 21% on semaglutide had already lost at least 15% by week 24. These "rapid responders" were more likely to reach every weight-loss threshold by week 72.8

Wegovy pill: how long does it take to work?

The Wegovy tablet starts at 1.5 mg a day, and the label steps it up every 30 days to the 25 mg maintenance dose from day 91.1 In the OASIS 4 trial of adults without diabetes, people on 25 mg lost 13.6% of their weight on average by week 64, vs 2.2% on placebo.13 More detail is in our article on oral semaglutide.

How long does Ozempic stay in your system?

~1 weekhalf-life of semaglutide (Wegovy, Ozempic labels)
~5 dayshalf-life of tirzepatide (Zepbound label)
5–7 weekssemaglutide still in the circulation after the last dose (Wegovy label)

Half-life is the time it takes for the level in the blood to fall by half. The Wegovy label says semaglutide will be present in the circulation for about 5 to 7 weeks after the last 2.4 mg or 7.2 mg injection or 25 mg tablet. The Ozempic label says about 5 weeks.1,3 The Zepbound label gives tirzepatide's elimination half-life as about 5 to 6 days in people with overweight or obesity, but does not state a total clearance time.2

This long tail matters for planning. The Wegovy label says to stop at least 2 months before a planned pregnancy because of the long half-life.1 See our article on GLP-1s, birth control and pregnancy, and talk to your care team. Appetite also tends to return once the medicine wears off, and trials show most lost weight comes back after stopping; here is what they found.

What this means day to day

  • Judge it in months, not days. In the trials, average weight was still coming down for about a year.
  • Look at the weekly trend. Daily weight swings with water and food. A weekly average shows the real direction.
  • Bring numbers to appointments. If you are worried about your pace or side effects, your prescriber can look at your weight trend and decide on next steps with you.

Common questions

How long does Ozempic take to work for weight loss?

In trials of semaglutide at the 2.4 mg weight-loss dose (sold as Wegovy), adults without diabetes had lost 10.6% of their body weight on average by week 20 in STEP 4 and 14.9% by week 68 in STEP 1. In those trials, weight kept coming down until about week 60.

How long does Zepbound take to work?

In an analysis of the SURMOUNT-1 trial of tirzepatide in adults without diabetes, 62.1% of participants had lost at least 5% of their weight by week 8. Average weight loss at week 72 was 15.0% to 20.9%, depending on dose.

How long does Ozempic stay in your system?

Semaglutide has a half-life of about 1 week. The Wegovy label says it stays in the circulation for about 5 to 7 weeks after the last dose, and the Ozempic label says about 5 weeks.

How long does the Wegovy pill take to work?

The Wegovy tablet label starts at 1.5 mg a day and steps up every 30 days, reaching the 25 mg maintenance dose from day 91. In the OASIS 4 trial, adults without diabetes on 25 mg lost 13.6% of their weight on average by week 64, vs 2.2% on placebo.

Does slow weight loss in the first two months mean it is not working?

Not necessarily. In a SURMOUNT-1 analysis, people on tirzepatide who had lost less than 5% by week 8 still lost 14.6% on average by week 72, and 69.1% of them reached at least 10%.

Sources

  1. WEGOVY (semaglutide) injection; WEGOVY (semaglutide) tablets. Prescribing information. Novo Nordisk; label revised 2026. DailyMed
  2. ZEPBOUND (tirzepatide) injection. Prescribing information. Eli Lilly; label revised 2026. DailyMed
  3. OZEMPIC (semaglutide) injection. Prescribing information. Novo Nordisk; label revised 2026. DailyMed
  4. Kokkinos A, Thethi T, Lee CJ, et al. Tirzepatide Efficacy and Tolerability According to Early Weight Response: A Post Hoc Analysis of the SURMOUNT-1 and SURMOUNT-2 Trials. Diabetes Obes Metab. 2026;28(9):8367-8377. PubMed · Full text (PMC)
  5. Blundell J, Finlayson G, Axelsen M, et al. Effects of once-weekly semaglutide on appetite, energy intake, control of eating, food preference and body weight in subjects with obesity. Diabetes Obes Metab. 2017;19(9):1242-1251. PubMed · Full text (PMC)
  6. Friedrichsen M, Breitschaft A, Tadayon S, et al. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes Obes Metab. 2021;23(3):754-762. PubMed · Full text (PMC)
  7. 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. PubMed · Full text (PMC)
  8. Aronne LJ, Horn DB, Kokkinos AD, et al. Relationship of early rapid weight loss to efficacy and safety of tirzepatide and semaglutide for obesity: SURMOUNT-5 post hoc analysis. Am J Med. 2026;139(7):913-921. PubMed · doi:10.1016/j.amjmed.2026.03.010
  9. Aronne LJ, Sattar N, Horn DB, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. JAMA. 2024;331(1):38-48. PubMed · Full text (PMC)
  10. Garvey WT, Batterham RL, Bhatta M, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nat Med. 2022;28(10):2083-2091. PubMed · Full text (PMC)
  11. Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed · doi:10.1056/NEJMoa2032183
  12. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PubMed · doi:10.1056/NEJMoa2206038
  13. Wharton S, Lingvay I, Bogdanski P, et al. Oral Semaglutide at a Dose of 25 mg in Adults with Overweight or Obesity (OASIS 4). N Engl J Med. 2025;393(11):1077-1087. PubMed · doi:10.1056/NEJMoa2500969
  14. Heise T, DeVries JH, Urva S, et al. Tirzepatide Reduces Appetite, Energy Intake, and Fat Mass in People With Type 2 Diabetes. Diabetes Care. 2023;46(5):998-1004. PubMed · Full text (PMC)
This article summarises published research for general information. It is not medical advice and does not replace advice from your own care team. Never change a medication or dose without talking to your prescriber.

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