Clinical trial averages applied to your weight — not a medical prediction, not a guarantee.
Head-to-head comparison of all three GLP-1 medication classes based on their respective clinical trial results at the highest approved dose. Enter your weight in My Projection first.
| Metric | Semaglutide Wegovy / Ozempic |
Tirzepatide Zepbound / Mounjaro |
Liraglutide Saxenda |
|---|
What does losing this weight actually mean for your health? Based on published secondary endpoints from GLP-1 clinical trials and general weight loss research. Enter your weight in My Projection first.
GLP-1 receptor agonists are a class of medications that mimic glucagon-like peptide-1, a hormone naturally produced in the gut that signals fullness, slows gastric emptying, and regulates blood sugar. Originally developed for type 2 diabetes management, these drugs have produced weight loss results in clinical trials that are unprecedented in the history of obesity pharmacology — outcomes previously achievable only with bariatric surgery. Understanding what the trials actually measured — and what they didn't — is essential for setting realistic expectations.
It is critical to understand that every percentage in this calculator comes from a specific published clinical trial, not manufacturer marketing. The STEP-1 trial for semaglutide (Wegovy) enrolled 1,961 adults and ran for 68 weeks under controlled conditions at the full 2.4mg weekly dose, with all participants receiving lifestyle counseling. The SURMOUNT-1 trial for tirzepatide enrolled 2,539 adults and ran for 72 weeks. Real-world results, without controlled lifestyle support and with the dose titration challenges many patients experience, typically run 10–30% below trial averages.
The STEP program consisted of four Phase 3 trials. STEP-1, the pivotal obesity trial, showed a mean weight loss of 14.9% of body weight (approximately 33 lbs for the average participant) over 68 weeks at the 2.4mg weekly dose. Critically, 86.4% of participants achieved at least 5% weight loss, 69.1% achieved at least 10%, and 50.5% achieved at least 15%. The range of responses was significant — some participants lost under 5% while others exceeded 20%. Ozempic (semaglutide 1mg, for diabetes) typically produces lower weight loss than Wegovy at the higher 2.4mg dose, averaging 6–9% in its own trials, but is widely used off-label for weight management.
Tirzepatide is a dual GIP/GLP-1 receptor agonist — it activates two hormone pathways rather than one. SURMOUNT-1 showed a mean weight loss of 20.9% at the 15mg dose over 72 weeks, with 91% of participants achieving at least 5% weight loss and 57% achieving at least 20%. At the 10mg dose the average was 19.5%, and at 5mg approximately 16%. These are the largest weight loss outcomes ever documented in a pharmacological trial. The SELECT trial (2023) further demonstrated that semaglutide reduces major cardiovascular events by 20% in people with pre-existing cardiovascular disease, independent of weight loss — a landmark finding that changed how these drugs are viewed clinically.
| Medication | Brand Name(s) | Avg Weight Loss | 5%+ Achieved | 15%+ Achieved | Trial Duration |
|---|---|---|---|---|---|
| Semaglutide 2.4mg | Wegovy | 14.9% | 86.4% | 50.5% | 68 weeks |
| Tirzepatide 15mg | Zepbound | 20.9% | 91.0% | 63.0% | 72 weeks |
| Liraglutide 3mg | Saxenda | 8.0% | 63.2% | 22.4% | 56 weeks |
| Semaglutide 1mg | Ozempic (diabetes) | 6–9% | ~70% | ~25% | 68 weeks |
Liraglutide at 3mg daily (Saxenda) was the first GLP-1 medication approved specifically for chronic weight management in 2014. The SCALE Obesity trial enrolled 3,731 adults and ran for 56 weeks, showing a mean weight loss of 8.0% of body weight. While modest compared to the newer agents, this represented a significant advance at the time, and liraglutide remains clinically relevant for patients who tolerate it well and cannot access the newer weekly injection medications due to cost, insurance, or supply constraints. Its daily injection requirement (versus weekly for semaglutide and tirzepatide) affects adherence for many patients.
This is arguably the most important clinical question about GLP-1 medications that most people don't ask before starting. The STEP-4 trial specifically studied discontinuation: participants who had lost an average of 10.6% of body weight on semaglutide over 20 weeks were then randomized to either continue or switch to placebo. Over the following 52 weeks, those who discontinued regained an average of two-thirds of their lost weight. By the end of the observation period, their body weight was roughly 5–6% below their original starting weight — meaningful, but substantially less than the maintained loss in the continuation group. This finding has important implications for understanding GLP-1 therapy as a chronic treatment for obesity rather than a short-term intervention. Obesity involves underlying hormonal and neurological dysregulation that these medications manage rather than cure — similar to how antihypertensive medications manage blood pressure without permanently fixing its underlying drivers.
The practical implication is significant: patients and prescribers should discuss a long-term treatment plan before starting, including what the strategy will be for maintenance, how supply and cost will be managed over years rather than months, and what role diet and exercise will play in sustaining results if medication is eventually reduced or discontinued. Patients who combine GLP-1 therapy with structured behavioral interventions — including dietary changes and exercise — tend to maintain more weight loss after discontinuation than those who relied on medication alone.
The range between the conservative and best-response projections in this calculator reflects real, documented variability in how individuals respond to GLP-1 medications. Several factors appear to influence response magnitude, though predicting individual outcomes remains impossible. Higher baseline BMI is generally associated with larger absolute weight loss but not necessarily larger percentage loss. Earlier response — significant weight loss in the first 4–12 weeks — is the strongest predictor of eventual total weight loss; patients who lose less than 5% in the first 12 weeks are significantly less likely to be strong responders at the full trial duration. Genetic factors including GLP-1 receptor variants likely explain some variability but are not yet clinically actionable in routine practice. Adherence to the full titration schedule, completion of dose escalation to the target dose without premature plateauing, and concurrent dietary changes all meaningfully affect the final outcome.
GLP-1 medications for weight management are FDA-approved for adults with a BMI of 30 or higher, or a BMI of 27 or higher with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or high cholesterol. They are prescription medications — you cannot obtain them without a licensed prescriber evaluating your individual health history, contraindications, and goals. Telehealth platforms have expanded access significantly, but legitimate prescribers will still conduct a medical intake, review your health history, and may require labs before prescribing.
The cost without insurance is substantial: Wegovy lists at approximately $1,350 per month, Zepbound at approximately $1,060 per month, and Saxenda at approximately $1,400 per month. Insurance coverage varies dramatically by plan. Many commercial insurance plans now cover at least one GLP-1 medication for obesity, but prior authorization is typically required. Manufacturer savings programs (Novo Nordisk's Wegovy Savings Card, Eli Lilly's Zepbound savings program) can reduce out-of-pocket costs to $25 per month for eligible commercially insured patients. Medicare currently does not cover GLP-1 medications for weight loss, though this is an active area of policy discussion.
Gastrointestinal side effects — nausea, vomiting, diarrhea, and constipation — are the most common, occurring in 40–80% of patients to some degree. These are typically most pronounced during dose escalation and improve significantly once at a stable maintenance dose. In the STEP-1 trial, 4.5% of semaglutide participants discontinued due to gastrointestinal side effects, compared to 0.8% on placebo. Serious adverse events are rare but real: pancreatitis has been reported at low rates, and there is a theoretical concern (based on animal studies, not demonstrated in humans) about thyroid C-cell tumors — which is why GLP-1 medications are contraindicated in patients with a personal or family history of medullary thyroid cancer or MEN2 syndrome.