Semaglutide Results Timeline: What STEP 1 Measured

Key findings at a glance

- In the STEP 1 trial, adults on semaglutide 2.4 mg lost a mean of 15.3 kg over 68 weeks versus 2.6 kg with placebo (Wilding et al., 2021). - Weight came off gradually, not in a burst: the trial raised the dose in steps over the first 16 weeks, and the group-average weight kept falling across the full 68 weeks (Wilding et al., 2021). - Half of the semaglutide group (50.5 percent) reached at least 15 percent weight loss by week 68, versus 4.9 percent on placebo (Wilding et al., 2021). - Research suggests weight loss on GLP-1 therapy tends to slow toward a plateau rather than continue without limit (Guo et al., 2025). - After treatment stopped in the STEP 1 extension, participants regained about two-thirds of the lost weight within a year (Wilding et al., 2022).

What is the semaglutide results timeline from the STEP 1 trial?

It is the reported group-average weight change measured across 68 weeks in STEP 1, one large randomized trial of semaglutide 2.4 mg (Wilding et al., 2021).

STEP 1 enrolled 1,961 adults with a BMI of 30 or higher, or 27 or higher with at least one weight-related condition, and without type 2 diabetes. Participants were randomized 2 to 1 to once-weekly semaglutide or placebo, and both groups also followed a reduced-calorie diet and increased physical activity (Wilding et al., 2021). Everything below describes what that population did on average. These are reported group means from one study, not a promise for any single person.

How did weight change week by week across the 68 weeks?

Weight declined gradually the whole way through, steep in the middle stretch and flattening near the end, after a stepwise dose increase over the first 16 weeks (Wilding et al., 2021).

The trial did not start at the full dose. It escalated over 16 weeks to reduce side effects, then held a maintenance dose to week 68.

The ranges below reflect what published studies and commonly studied research protocols report. This is educational, not a prescription or a personal recommendation.

Source: Wilding et al., 2021.

Mapping the reported weight trend onto those phases:

Source: Wilding et al., 2021.

How much weight did the semaglutide group lose overall?

The semaglutide group lost a mean of 15.3 kg, about 14.9 percent of body weight, versus 2.6 kg, about 2.4 percent, with placebo over 68 weeks (Wilding et al., 2021).

That works out to a difference of roughly 12.4 percentage points between the two groups at week 68 (Wilding et al., 2021). The trial also reported improvements in waist circumference and several cardiometabolic markers alongside the weight change (Wilding et al., 2021).

What share of participants reached each weight-loss milestone?

More than eight in ten reached at least 5 percent loss, and half reached at least 15 percent (Wilding et al., 2021).

Source: Wilding et al., 2021.

About a third of the semaglutide group reached 20 percent or more (Wilding et al., 2021). The spread across these milestones is the point: the 15.3 kg mean sits on top of a wide range of individual outcomes, so a group average does not describe what one person will do.

Why does the weight-loss curve slow down and plateau?

Weight loss on GLP-1 therapy typically decelerates over time and settles toward a plateau, partly because the body's energy use adapts as weight falls (Guo et al., 2025; Rosenbaum and Leibel, 2010).

In STEP 1 the group-mean curve was still declining late in the trial but was flatter near week 68 than at the midpoint (Wilding et al., 2021). A model-based meta-analysis of GLP-1 therapy reported that the time to reach an efficacy plateau varied by drug, from about 17 weeks for liraglutide to about 46 weeks for the dual agonist tirzepatide, the slowest; the same analysis reported that semaglutide had not yet reached its plateau by 52 weeks (Guo et al., 2025; Obesity Pillars 2025; doi:10.1016/j.obpill.2025.100162). Adaptive thermogenesis, the drop in energy expenditure that follows weight loss, is one reported reason the pace slows (Rosenbaum and Leibel, 2010; Int J Obes 2010).

What happened after participants stopped semaglutide?

In the STEP 1 extension, participants regained about two-thirds of their lost weight within a year of stopping the drug and the lifestyle program (Wilding et al., 2022).

Cardiometabolic markers that had improved also moved back toward baseline (Wilding et al., 2022). A similar regain pattern after withdrawing a GLP-1-class drug was reported for tirzepatide in SURMOUNT-4 (Aronne et al., 2024). The takeaway from the data is that the reported timeline reflects continued treatment, and the trajectory changed once treatment ended.

How does the semaglutide timeline compare with tirzepatide?

Separate trials reported larger group-mean loss for tirzepatide, but the studies used different designs and populations, so the timelines are not directly comparable (Jastreboff et al., 2022; Frias et al., 2021).

SURMOUNT-1 reported up to about 22.5 percent mean weight loss with tirzepatide in adults with obesity and without diabetes (Jastreboff et al., 2022), while SURPASS-2 compared tirzepatide with a 1.0 mg dose of semaglutide in adults with type 2 diabetes, a different setting from STEP 1 (Frias et al., 2021). Newer class data, such as retatrutide reporting up to about 24.2 percent at 48 weeks, sits in yet another trial design (Jastreboff et al., 2023). Cross-trial numbers are useful for context, not for a like-for-like race.

What doses did STEP 1 use, and what does that mean for me?

STEP 1 escalated to a 2.4 mg once-weekly maintenance dose, but that is a reported research protocol, not a personal instruction, and any dose decision belongs with a qualified clinician.

The dose schedule in the table above describes what the trial did, framed as research reported. It is not guidance on what to take, when, or how. This page is educational and describes published findings. It does not diagnose, treat, or prevent anything, and it does not promise a result. A licensed clinician who knows your history is the correct source for any personal decision.

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