Medically reviewed by a licensed healthcare professional. Last updated March 2026.
Key Takeaways
- Clinical trials show average weight loss of 14.9% (semaglutide) to 22.5% (tirzepatide) over 68-72 weeks [1][2].
- A 200-pound person can expect to lose approximately 30-45 pounds over 12-18 months at the target dose.
- Most weight loss occurs during months 3-12, after reaching higher doses.
- Individual results vary widely — some patients lose significantly more or less than averages.
- Combining medication with diet and exercise consistently produces better results.
What the Clinical Trials Show
The most reliable weight loss data comes from large, randomized controlled trials. Here's what the evidence demonstrates:
Semaglutide (Wegovy) — STEP 1 Trial [1]
- Participants: 1,961 adults with obesity (BMI 30+) or overweight with comorbidities
- Duration: 68 weeks
- Average weight loss: 14.9% of body weight (vs. 2.4% placebo)
- Achieved 5% loss: 86% of participants
- Achieved 10% loss: 69% of participants
- Achieved 15% loss: 50% of participants
- Achieved 20% loss: 32% of participants
Tirzepatide (Zepbound) — SURMOUNT-1 Trial [2]
- Participants: 2,539 adults with obesity (BMI 30+) or overweight with comorbidities
- Duration: 72 weeks
- Average weight loss (highest dose): 22.5% of body weight (vs. 3.1% placebo)
- Achieved 5% loss: 96% of participants
- Achieved 10% loss: 89% of participants
- Achieved 20% loss: 63% of participants
- Achieved 25% loss: 39% of participants
Realistic Weight Loss by Starting Weight
Trial averages are useful but what does this mean for you? Here are projections based on starting weight:
On Semaglutide (~15% average loss)
| Starting Weight | Expected Loss (12-18 mo) | Expected Final Weight |
|---|---|---|
| 180 lbs | 25-30 lbs | 150-155 lbs |
| 200 lbs | 28-32 lbs | 168-172 lbs |
| 220 lbs | 30-35 lbs | 185-190 lbs |
| 250 lbs | 35-40 lbs | 210-215 lbs |
| 300 lbs | 42-48 lbs | 252-258 lbs |
On Tirzepatide (~20-22% average loss)
| Starting Weight | Expected Loss (12-18 mo) | Expected Final Weight |
|---|---|---|
| 180 lbs | 34-40 lbs | 140-146 lbs |
| 200 lbs | 38-45 lbs | 155-162 lbs |
| 220 lbs | 42-50 lbs | 170-178 lbs |
| 250 lbs | 48-56 lbs | 194-202 lbs |
| 300 lbs | 57-68 lbs | 232-243 lbs |
Important caveat: These are projections based on trial averages. Individual results vary significantly. Some patients lose more than double the average; others lose less than half.
Timeline: When Does Weight Loss Happen?
Weight loss on GLP-1 medications follows a predictable pattern tied to the dose escalation schedule:
Months 1-2: Adjustment Phase
- Dose: 0.25 mg → 0.5 mg (semaglutide)
- Weight loss: 2-5% of body weight
- Primary driver: Reduced appetite and calorie intake
Months 3-6: Acceleration Phase
- Dose: 1.0 mg → 1.7 mg → 2.4 mg (semaglutide)
- Weight loss: 5-12% cumulative
- This is when most patients see the most dramatic changes
- Weekly losses of 1-3 pounds are common
Months 6-12: Maximum Effect Phase
- Dose: Maintenance at target dose
- Weight loss: 12-20%+ cumulative
- Weight loss rate begins to slow as you approach a new equilibrium
- Body is adapting to its new weight set point
Months 12-18: Plateau and Maintenance
- Weight loss typically plateaus between months 12-18
- This is not failure — it's your body reaching a new stable weight
- Maintaining the loss requires ongoing medication
Factors That Affect Your Results
Factors That Increase Weight Loss
- Higher starting BMI: Patients with higher starting weights tend to lose more absolute weight
- Consistent medication use: Missing doses reduces effectiveness
- Dietary changes: Focusing on protein-rich, whole foods amplifies results
- Physical activity: Regular exercise — especially resistance training — preserves muscle mass and boosts metabolism
- Adequate sleep: Poor sleep is associated with reduced weight loss
- Reaching the target dose: Patients who tolerate the full maintenance dose lose more than those who stay at lower doses
Factors That Reduce Weight Loss
- Medications that promote weight gain: Some antidepressants, antipsychotics, insulin, and corticosteroids can counteract GLP-1 effects
- Medical conditions: Hypothyroidism, PCOS, Cushing's syndrome, and other endocrine disorders
- Alcohol consumption: High-calorie and can trigger overeating
- Stress eating: GLP-1 medications reduce physical hunger but may not fully address emotional eating
- Not reaching target dose: Staying at lower doses due to side effects limits weight loss potential
What About Plateaus?
Weight loss plateaus are normal and expected. Your body is not a machine — it adapts to changes in calorie intake and weight. Here's what to know:
A plateau is not the medication "stopping working." It means your body has reached a new energy balance at your current dose and calorie intake.
Strategies for Breaking Through
- Review your eating habits — Portions can creep up over time without noticing
- Add or increase exercise — Even adding a daily 30-minute walk can make a difference
- Discuss dose adjustment — Your provider may adjust timing or dosing
- Focus on non-scale victories — Body composition changes (losing fat, preserving muscle) continue even when the scale doesn't move
- Be patient — Plateaus often resolve on their own after 2-4 weeks
Maintaining Your Results
The evidence on weight maintenance after GLP-1 discontinuation is clear: most patients regain a significant portion of lost weight within 1-2 years of stopping medication [3].
The STEP 1 extension study found that participants who discontinued semaglutide regained approximately two-thirds of their lost weight within one year [3]. This is not a medication failure — it reflects the chronic nature of obesity as a disease.
Current best practice: Continue medication at a maintenance dose long-term, combined with healthy eating and regular physical activity. Discuss your long-term treatment plan with your provider.
Find a GLP-1 provider who will support your long-term goals, or explore telehealth options for convenient ongoing care.
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Individual results vary. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you are experiencing a medical emergency, call 911.
Sources
- Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)." New England Journal of Medicine. 2021;384:989-1002.
- Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)." New England Journal of Medicine. 2022;387:205-216.
- Wilding JPH, et al. "Weight Regain and Cardiometabolic Effects after Withdrawal of Semaglutide (STEP 1 Extension)." Diabetes, Obesity and Metabolism. 2022;24:1553-1564.