Medically reviewed by a licensed healthcare professional. Last updated March 2026.

What the Clinical Trials Show

The most reliable weight loss data comes from large, randomized controlled trials. Here's what the evidence demonstrates:

Key Takeaways
  • Clinical trials show average weight loss of 14.9% (semaglutide) to 22.5% (tirzepatide) over 68-72 weeks .
  • 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.

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

  1. Review your eating habits — Portions can creep up over time without noticing
  2. Add or increase exercise — Even adding a daily 30-minute walk can make a difference
  3. Discuss dose adjustment — Your provider may adjust timing or dosing
  4. Focus on non-scale victories — Body composition changes (losing fat, preserving muscle) continue even when the scale doesn't move
  5. Be patient — Plateaus often resolve on their own after 2-4 weeks
Good to Know

GLP-1 medications require a prescription and ongoing medical supervision. Always work with a licensed healthcare provider and verify that any telehealth platform or clinic uses board-certified clinicians and accredited pharmacies.

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.

Ready to start your weight loss journey? Find a GLP-1 clinic near you and connect with a qualified provider today.

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.

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Sources

  1. Wilding JPH, et al. "Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1)." New England Journal of Medicine. 2021;384:989-1002.
  2. Jastreboff AM, et al. "Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)." New England Journal of Medicine. 2022;387:205-216.
  3. Wilding JPH, et al. "Weight Regain and Cardiometabolic Effects after Withdrawal of Semaglutide (STEP 1 Extension)." Diabetes, Obesity and Metabolism. 2022;24:1553-1564.