If you are considering a GLP-1 medication for weight loss, the most important question is: how much weight will I actually lose? Here is what the clinical trial data says at 3 months, 6 months, and 12+ months.
Wegovy (Semaglutide 2.4 mg) — STEP Program Results
The STEP clinical trial program included four phase 3 trials with over 4,500 participants. The data shows a consistent pattern of weight loss over time.
STEP 1: 68-Week Results
Published in NEJM (Wilding et al., 2021), STEP 1 showed that weight loss with semaglutide follows a predictable trajectory:
- Week 4: Weight loss begins within the first month
- Week 28 (6 months): Majority of weight loss achieved — approximately 11-12% of body weight
- Week 60-68 (12-15 months): Nadir reached — 14.9% average total weight loss
- Weight regained after stopping: Approximately two-thirds of lost weight regained within 1 year of discontinuation
At 68 weeks, 86.4% of participants lost at least 5% of their body weight, 69.1% lost at least 10%, 50.5% lost at least 15%, and 32% lost at least 20%. The average participant lost 15.3 kg (33.7 lbs).
Zepbound (Tirzepatide) — SURMOUNT Program Results
The SURMOUNT trials show significantly higher weight loss with tirzepatide:
SURMOUNT-1: 72-week trial with 2,539 participants (Jastreboff et al., NEJM 2022):
- 15 mg dose: 22.5% average weight loss (52 lbs)
- 10 mg dose: 21.4% (49 lbs)
- 5 mg dose: 16.0% (35 lbs)
- 91% of participants lost at least 5% of body weight
- 57% lost at least 20% of body weight
SURMOUNT-2: In people with type 2 diabetes and obesity, tirzepatide led to 15.7% weight loss at 72 weeks (Garvey et al., The Lancet, 2023).
SURMOUNT-3 and SURMOUNT-4: Showed that tirzepatide continued to produce weight loss after an initial intensive lifestyle intervention period, and that maintaining treatment was essential for keeping weight off.
Timeline: What to Expect Month by Month
Month 1-2: Initial weight loss begins within 2-4 weeks. Most people lose 2-5% of body weight during the dose escalation period. Gastrointestinal side effects are most common here.
Month 3-6: Steady weight loss of 0.5-1% of body weight per week. At 6 months, most patients have lost 10-15% of starting weight on tirzepatide, or 8-12% on semaglutide.
Month 6-12: Weight loss continues but at a slower rate. Peak weight loss is typically reached between months 8-12 and then plateaus.
After 12 months: Weight is maintained as long as the medication is continued. If stopped, significant weight regain is expected.
Key Factors That Affect Results
- Starting weight: Higher starting BMI correlates with greater absolute weight loss
- Diet and exercise: Participants in the trials all received lifestyle counseling — the drug alone will not produce maximum results
- Dose: Higher doses produce more weight loss, but side effects may limit tolerability
- Consistency: Skipping doses reduces effectiveness
References:
1. Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. NEJM 2021;384:989-1002.
2. Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity. NEJM 2022;387:205-216.
3. Garvey WT, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2). The Lancet 2023;402:613-626.
4. Wadden TA, et al. Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity (SURMOUNT-3). Nature Medicine 2023.