The endpoints everyone should know before starting
Four large randomized controlled trials define what to realistically expect on GLP-1 therapy. If you start a medication without understanding these numbers, you will set unrealistic short-term goals and give up during the titration plateau:
- STEP 1 (Wilding et al., NEJM 2021): semaglutide 2.4 mg weekly vs placebo in adults with overweight/obesity without diabetes. N=1,961, 68 weeks. Mean TBWL: 14.9% on semaglutide vs 2.4% on placebo. 86% of semaglutide participants achieved ≥5% TBWL; 50% achieved ≥15%.
- STEP 2 (Davies et al., 2021): semaglutide in T2D cohort. TBWL at week 68: 9.6% on 2.4 mg, 7.0% on 1.0 mg. Slightly lower than the non-diabetes cohort, as expected.
- SURMOUNT-1 (Jastreboff et al., NEJM 2022): tirzepatide 5/10/15 mg vs placebo. N=2,539, 72 weeks. Mean TBWL: 15.0% on 5 mg, 19.5% on 10 mg, 22.5% on 15 mg vs 3.1% on placebo. 96% of 15 mg participants achieved ≥5%, 63% achieved ≥20%.
- SCALE Obesity and Prediabetes: liraglutide 3.0 mg daily in adults with BMI ≥ 30 or ≥ 27 with comorbidity. 56 weeks, mean TBWL ~8%.
The shape of the curve, month by month
Trial data shows a characteristic saturating curve, not a linear descent. Approximate expectations on the top dose, with good tolerance and standard titration:
- Month 1 (weeks 1–4, starter dose): 2–4 lb, mostly appetite dampening and water.
- Month 3 (week 12, therapeutic dose reached): 5–8% TBWL on semaglutide, 7–10% on tirzepatide 10 mg.
- Month 6 (week 24): 9–12% on semaglutide, 13–17% on tirzepatide 15 mg.
- Month 9 (week 36): 12–14% on semaglutide, 18–20% on tirzepatide 15 mg.
- Month 12 (week 52): 13–16% on semaglutide 2.4 mg, 20–22% on tirzepatide 15 mg.
- Month 16–18 (nadir): 14–15% semaglutide; 22–23% tirzepatide.
Why the first 8 weeks feel slow
The titration schedule is designed to minimize GI side effects, but the tradeoff is that you are not on a therapeutic dose in month 1. A 225 lb patient on week 3 of 0.25 mg semaglutide should expect 2–5 lb loss, and much of that is glycogen-bound water. It is not that the drug isn’t working — it is that you are still in the ramp. See the dosage-schedule generator for when you hit each step.
What drives individual variance from trial means
Trial mean TBWL is a central tendency, not a promise. The distribution is wide. In STEP 1, 13% of participants did not achieve ≥5% TBWL (“non-responders”). In SURMOUNT-1, 9% did not reach 5% on 15 mg tirzepatide. Factors that predict being above or below the mean:
- Starting BMI: higher BMI patients lose more absolute pounds but often similar percentages.
- Tolerance of escalation: patients who can reach and maintain the top dose (2.4 mg sema, 15 mg tirz) hit the ceiling; patients who plateau at a submaximal dose lose correspondingly less.
- Adherence: a 2024 claims-data analysis of real-world GLP-1 prescriptions showed <25% of commercial claims completed 12 months continuous therapy. Real-world mean TBWL is meaningfully lower than trial mean because of discontinuation.
- Baseline diet and activity: patients who layer a structured diet intervention (see the diet tool) and resistance training (exercise on GLP-1) onto the medication outperform the drug-alone trial arms.
- T2D status: T2D cohorts lose ~30–40% less on the same drug than non-diabetic cohorts. STEP 2 vs STEP 1.
- Concurrent medications: SSRIs, certain antipsychotics (olanzapine), and some mood stabilizers blunt weight loss on GLP-1.
- Genetics / pharmacogenomics: emerging data suggests GLP-1R polymorphisms explain some variance; not clinically actionable yet.
Waist circumference moves differently than scale weight
Weekly waist-circumference measurement (morning fasted, at the navel, tape level) is a cleaner signal of visceral fat loss than the scale and usually leads scale-weight trends by 1–2 weeks. STEP 1 reported a mean waist reduction of 13.5 cm at week 68 on semaglutide 2.4 mg — roughly 5.3 inches. SURMOUNT-1 reported 17.8 cm (7.0 in) on tirzepatide 15 mg. Waist reductions of 2 cm/month during therapeutic-dose months are on-target; < 1 cm/month for 3 consecutive months is a signal to troubleshoot (adherence, protein, sleep, stress-driven cortisol). DEXA every 3–6 months adds rigor ($100–$250 cash); it splits fat mass, lean mass, and bone mineral and lets you see body composition, not just total mass.
The plateau, and what to do about it
Plateau is predictable. For semaglutide, it typically arrives around week 40–50; for tirzepatide 15 mg, week 50–60. This is the drug’s dose ceiling, not a failure. Options:
- Switch drugs: semaglutide to tirzepatide is the most common move when additional loss is desired. Expect an additional 5–7% TBWL.
- Accept the new set point: most patients’ clinical goals are met by 15–20% TBWL regardless of ideal body weight. SELECT’s CV benefit kicked in at ~9% TBWL.
- Combination therapy: metformin, bupropion-naltrexone (Contrave), or phentermine-topiramate (Qsymia) can be layered under specialist supervision.
- Review adherence and inputs: often the apparent plateau is creep in calorie intake as appetite suppression partly adapts. See the plateau breaker tool.
Body composition under the weight-loss curve
The scale tells you how much mass you have lost; it does not tell you what you lost. DEXA substudies from STEP and SURMOUNT programs consistently show that 20–40% of the mass lost on GLP-1 monotherapy is lean tissue — higher than the ~25% seen in structured bariatric-surgery cohorts and dramatically higher than the <15% typical of resistance-training-plus-high-protein programs. The practical consequences: at 22.5% TBWL from a 225 lb starting weight (50 lb total), 10–15 lb of that may be fat-free mass. That lean-mass loss can drop resting metabolic rate by 100–200 kcal/day and accelerates sarcopenia risk, especially in patients over 55. The countermeasure is not mysterious: 1.6–2.2 g/kg ideal body weight of protein per day and 2–4 resistance sessions per week covering squat, hinge, push, pull, and carry patterns. The protein target tool and exercise on GLP-1 calculators work the specifics. Patients who layer both interventions onto the drug consistently outperform drug-alone arms on fat-mass loss and preserve lean mass closer to 90%.
SELECT, STEP-HFpEF, and the “non-weight” value
If you are not tracking the cardiovascular and heart-failure read-outs, the timeline conversation is incomplete. SELECT (Lincoff et al., NEJM 2023, N=17,604 adults with established CVD and BMI ≥ 27, no T2D) showed a 20% relative reduction in the primary composite of CV death, non-fatal MI, and non-fatal stroke over ~40 months on semaglutide 2.4 mg. STEP-HFpEF and STEP-HFpEF DM (McMurray et al., 2023 and 2024) in patients with heart failure with preserved ejection fraction and obesity showed semaglutide improved KCCQ-CSS symptom score by ~7–9 points and 6-minute walk distance by 17–21 meters vs placebo. SELECT’s effect appeared to be only partly mediated by weight loss, implying direct cardiovascular mechanism (plaque stabilization, anti-inflammatory effect, blood-pressure reduction). For patients whose weight trajectory is the primary motivation, these are side benefits; for patients with established CVD or HFpEF, they are co-primary outcomes. FDA added the CV risk-reduction indication to Wegovy’s label in March 2024 and that label change is what opened Medicare Part D coverage for the SELECT cohort.
What happens when you stop
STEP 4 (the withdrawal arm) randomized patients who had completed 20 weeks of semaglutide 2.4 mg to either continue or switch to placebo. Over the next 48 weeks, continuers lost another 8% on top of initial loss; placebo switchers regained roughly two-thirds of lost weight. The conclusion is clinical and unambiguous: GLP-1 therapy is a chronic treatment. Plan accordingly. See the stopping GLP-1 regain projector.
FAQ
How much will I lose in the first month on Wegovy?
Typically 2–5 lb at the 0.25 mg starter dose — not a therapeutic dose. Do not judge the drug by the first month.
Will I lose more on Zepbound than Wegovy?
On average yes. SURMOUNT-1 showed 22.5% TBWL on tirzepatide 15 mg at week 72 vs 14.9% for semaglutide 2.4 mg at week 68 in STEP 1 (indirect comparison). SURMOUNT-5 (tirzepatide 15 mg vs semaglutide 2.4 mg head-to-head) confirmed superiority. See the Wegovy vs Zepbound comparison.
Why isn’t my loss matching the STEP 1 curve?
Because STEP 1 enrolled patients without diabetes, with good adherence, and measured mean TBWL in the per-protocol population. Real-world factors — T2D, adherence gaps, concomitant medications — predictably shift individual results. If you are 3+ percentage points below expected at month 6 on top dose, discuss with your prescriber.
Is faster loss better?
No. Faster loss correlates with more lean-mass loss. Aim for 1–2 lb/week during therapeutic-dose months and accept slower during titration and maintenance. Protect muscle via resistance training and protein.
Do I need to stay on the drug after I reach my goal?
For most patients, yes. GLP-1 is a chronic treatment for a chronic disease. Some patients successfully taper to lower maintenance doses. See the maintenance dose tool.