The four GLP-1 drugs: what they are and how they differ
The four medications most commonly discussed are Ozempic, Wegovy, Mounjaro, and Zepbound. Understanding the distinctions matters because they affect expected timelines and outcomes.
- Ozempic (semaglutide, Novo Nordisk): Approved for type 2 diabetes management. Frequently prescribed off-label for weight loss. Maximum approved dose: 2mg weekly. A GLP-1 receptor agonist — targets one receptor type.
- Wegovy (semaglutide, Novo Nordisk): The same molecule as Ozempic but at a higher dose — 2.4mg weekly. Specifically FDA-approved for chronic weight management in adults with obesity or overweight with at least one weight-related condition.
- Mounjaro (tirzepatide, Eli Lilly): Approved for type 2 diabetes. Prescribed off-label for weight loss. A dual GIP/GLP-1 receptor agonist — targets two receptor types, which is the primary reason it produces greater weight loss than semaglutide in trials.
- Zepbound (tirzepatide, Eli Lilly): Same molecule as Mounjaro, approved specifically for chronic weight management at the same doses (up to 15mg weekly).
The key clinical distinction is the receptor mechanism. Semaglutide (Wegovy/Ozempic) activates GLP-1 receptors only. Tirzepatide (Mounjaro/Zepbound) activates both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP receptor activation appears to enhance the appetite-suppressing and metabolic effects of GLP-1 agonism, producing the meaningfully superior weight loss outcomes seen in the SURMOUNT trials versus the STEP trials.
The STEP trials: semaglutide weight loss data
The STEP (Semaglutide Treatment Effect in People with obesity) trials were a series of large Phase 3 randomised controlled trials conducted by Novo Nordisk, with results published primarily in The New England Journal of Medicine between 2021 and 2022.
STEP 1 (Wilding et al., NEJM, 2021): 1,961 adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related condition, randomised to semaglutide 2.4mg or placebo for 68 weeks. Primary result: −14.9% mean body weight loss with semaglutide vs −2.4% with placebo. 86.4% of participants achieved at least 5% weight loss; 69.1% achieved at least 10%; 50.5% achieved at least 15%.
STEP 2 (Davies et al., The Lancet, 2021): Participants with type 2 diabetes — a harder-to-treat population — achieved mean weight loss of −9.6% with semaglutide 2.4mg over 68 weeks, demonstrating that metabolic context affects outcomes.
The titration schedule for Wegovy/semaglutide is as follows: starting at 0.25mg weekly for 4 weeks, increasing by 0.25mg every 4 weeks until reaching the 2.4mg maintenance dose at week 16. This means the full therapeutic dose is not active until week 17 — a critical fact for setting realistic early expectations.
Weeks 1–16 on Wegovy/semaglutide are dose titration — you are not on the full therapeutic dose until week 17. Slow initial loss does not mean the medication is not working. The peak loss rate occurs between months 4 and 8, once the full dose has been established for several weeks.
The SURMOUNT trials: tirzepatide weight loss data
The SURMOUNT trials were Eli Lilly's Phase 3 programme for tirzepatide in obesity, with the landmark SURMOUNT-1 results published in The New England Journal of Medicine in 2022.
SURMOUNT-1 (Jastreboff et al., NEJM, 2022): 2,539 adults with obesity or overweight randomised to tirzepatide 5mg, 10mg, 15mg, or placebo for 72 weeks. Primary results: mean weight loss of −15.0% at 5mg, −19.5% at 10mg, and −20.9% at 15mg, versus −3.1% for placebo. At the 15mg dose, 91% of participants achieved at least 5% weight loss, 79% achieved at least 15%, and 55% achieved at least 20%.
SURMOUNT-2 (Garvey et al., The Lancet, 2023): Participants with type 2 diabetes achieved mean weight loss of −13.4% at 10mg and −15.7% at 15mg over 72 weeks — again demonstrating that diabetes reduces the magnitude of response, but tirzepatide still substantially outperforms semaglutide in this population.
The tirzepatide titration schedule starts at 2.5mg weekly for 4 weeks, increasing by 2.5mg every 4 weeks, with a maximum dose of 15mg reached at week 20. The titration is slower than semaglutide's — weight loss in the first 8–12 weeks is modest, and comparisons between drugs at early time points systematically understate tirzepatide's eventual superiority.
Week-by-week weight loss comparison table
The following figures are derived from published trial data and represent mean percentage body weight loss from baseline at each time point. Individual results vary substantially.
| Time point | Wegovy (semaglutide 2.4mg) | Ozempic (semaglutide 1mg, off-label) | Mounjaro/Zepbound (tirzepatide 15mg) |
|---|---|---|---|
| Week 4 | ~−1.5% | ~−1.0% | ~−1.5% |
| Week 8 | ~−3.5% | ~−2.5% | ~−3.5% |
| Week 16 | ~−6.5% | ~−4.5% | ~−7.5% |
| Week 28 | ~−10.5% | ~−7.0% | ~−14.0% |
| Week 40 | ~−13.0% | ~−8.5% | ~−18.0% |
| Week 52 (1 year) | ~−14.0% | ~−9.5% | ~−20.0% |
| Week 68–72 (trial end) | −14.9% STEP 1 | ~−10–11% | −20.9% SURMOUNT-1 |
For a person starting at 100kg (220 lbs), these percentages translate to approximately: Wegovy — 14.9kg (33 lbs) lost over 68 weeks; tirzepatide 15mg — 20.9kg (46 lbs) lost over 72 weeks. The absolute difference is significant, but both represent substantial improvements over placebo and over previously available treatments.
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Track your GLP-1 weight loss journey week by week. tr8ck's dedicated GLP-1 module logs your progress, side effects, and correlations — so you always know how your response compares to expected timelines.
Start tracking free →When plateaus happen — and why
A weight loss plateau is one of the most common and demoralising experiences for people on GLP-1 medications. Understanding when and why they occur makes them less alarming and more actionable.
The physiological plateau. In the STEP 1 trial, the rate of weight loss was fastest between weeks 16 and 32 (months 4–8), after the full dose was established. After week 32, the weekly rate of loss slowed considerably, and weight essentially stabilised between weeks 56 and 68. This is expected — as body weight decreases, so does total daily energy expenditure, which narrows the caloric deficit produced by the same level of appetite suppression.
The calorie drift plateau. GLP-1 medications suppress appetite, but appetite can partially adapt over months. Some people experience a gradual drift in calorie intake back toward their pre-medication baseline, particularly for highly palatable processed foods. This is distinct from the physiological plateau and is addressable through nutritional awareness and consistent food logging.
The dose-change plateau. During dose titration steps (every 4 weeks early in treatment), weight loss can temporarily slow as the body adjusts to the new dose before the full effect of the higher dose is established. This is normal and does not indicate treatment failure.
The stress and sleep plateau. Psychosocial stress, sleep deprivation, and major life events can temporarily blunt the appetite-suppressing effects of GLP-1 medications and increase cortisol — a hormone associated with increased appetite and fat retention. A plateau coinciding with a period of high stress or poor sleep is a specific pattern that tr8ck's GLP-1 tracking module can surface by correlating weight trend against sleep and mood data.
Why individual tracking is essential on GLP-1 medications
Clinical trial data tells you what happened on average across thousands of participants. It cannot tell you what is happening in your specific body, at your specific dose, with your specific diet, sleep, and activity patterns.
Individual responses to GLP-1 medications vary enormously. In the STEP 1 trial, while the mean weight loss was 14.9%, the range was 0% to more than 30%. Some people at the same dose of the same drug achieve twice the average result; others achieve half. The drug is the same. The person is not.
Tracking daily weight, food intake, sleep, mood, and side effects together lets you:
- Know whether your progress is on track against the expected timeline, not just against a vague sense of whether you "feel" like it's working.
- Identify plateaus early — a 7-day rolling average trend that has flattened for 3+ weeks is a plateau. A single bad weigh-in day is noise. Tracking shows you the difference.
- Connect side effects to specific triggers. Nausea, food aversions, and GI discomfort are common on GLP-1 medications and often linked to specific food types, meal sizes, or timing. Logging what you ate alongside a side effect rating makes these patterns visible within 2–3 weeks.
- Bring data to your prescriber. "I've plateaued" is anecdote. "My 7-day rolling average weight has been flat for 4 weeks, my calorie intake has held steady at approximately 1,600 kcal/day, and my sleep average is 6.5 hours versus 7.5 hours two months ago" is a clinical conversation starter.
tr8ck's GLP-1 module is purpose-built for this. It tracks weight trend, side effect logging, food intake, sleep, and mood in one place — and runs the correlation analysis that reveals whether lifestyle variables like sleep are affecting your medication's response.
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Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. GLP-1 medications are prescription drugs. Always consult a qualified healthcare professional before starting, stopping, or adjusting any medication. Clinical trial data represents population averages — individual results vary significantly.