Key finding: Real-world GLP-1 patients lose substantially less weight than clinical trial subjects. Wegovy patients in 2024-2025 real-world studies averaged 9.1 percent weight loss at 12 months vs 14.9 percent in the STEP 1 trial. Zepbound real-world averages 12.4 percent vs 20.9 percent in SURMOUNT 1. The 5 to 8 percentage point gap is driven by lower adherence, faster discontinuation, and slower dose escalation outside controlled trials.
Not medical advice. Original analysis of published real-world evidence studies and pharmaceutical industry data.
Clinical trial vs real-world weight loss outcomes
Medication
Clinical trial loss at 12mo
Real-world loss at 12mo
Gap
Source
Wegovy 2.4mg (semaglutide)
14.9% (STEP 1)
9.1%
-5.8pp
Gleason et al, Truveta 2024 (n=7,881)
Ozempic 1.0mg (semaglutide T2D)
6.5kg (SUSTAIN 7)
4.2kg
-35%
Epic Cosmos 2024 (n=24,400)
Zepbound 15mg (tirzepatide)
20.9% (SURMOUNT 1)
12.4%
-8.5pp
Truveta tirzepatide cohort 2024 (n=3,624)
Mounjaro 15mg (T2D)
12.9kg (SURPASS 3)
8.7kg
-33%
Komodo Health 2024 (n=18,200)
What drives the trial vs real-world gap
Four factors account for almost the entire performance gap between clinical trial outcomes and real-world patient outcomes.
Factor
Clinical trial
Real world
12-month adherence rate
87-92%
32-42%
Reach maintenance dose
95%
58%
Discontinuation by month 12
8%
38-58%
Concurrent lifestyle counseling
Required (per protocol)
~15% receive any
Why patients quit GLP-1 medications
37%. Cost: Out-of-pocket pricing of $1,000-$1,800/month is the #1 reason.
28%. Side effects: Persistent nausea, GI issues, or fatigue.
18%. Reached goal weight: Often followed by regain (averaging 67% regain within 12 months of stopping per STEP 4 extension data).
12%. Insurance change: Lost coverage or formulary changed.
5%. Other: Including supply shortages 2022-2024.
Adherence correlates directly with weight loss outcomes
Real-world weight loss outcomes scale linearly with adherence. The Truveta 2024 Wegovy cohort segmented by adherence shows:
Patients with >80% adherence: 13.7% weight loss at 12mo (close to trial 14.9%)
Patients with 60-80% adherence: 10.4% weight loss
Patients with 40-60% adherence: 6.8% weight loss
Patients with
The 5.8 percentage point gap between real-world average (9.1%) and trial outcome (14.9%) is almost entirely explained by the difference in adherence between trial subjects (87-92%) and real-world patients (32-42%).
What helps close the gap
Three interventions show measurable real-world benefit in published 2024-2025 evidence:
Structured nutrition support: Patients enrolled in registered dietitian programs alongside GLP-1 medication achieve 11.8% weight loss vs 7.4% without (Komodo Health 2024 sub-analysis).
Meal delivery + GLP-1: Anecdotal but consistent in patient surveys. Factor and Trifecta both report 30%+ YoY growth in GLP-1 user segment 2024-2025.
Resistance training 2-3x/week: Reduces lean mass loss from 25-39% of total weight lost to 12-15% (multiple Lancet sub-analyses).
Implications for patients
If you are on a GLP-1 medication, the data say three things:
Plan for real-world outcomes, not trial outcomes. Realistic expectation: 8-12% body weight loss at 12 months on Wegovy, 11-14% on Zepbound. Anything above that is a bonus.
Adherence is the single biggest controllable factor. Missing weekly doses costs more weight loss than any food choice you can make.
Structured nutrition support matters. Either a dietitian or a structured meal delivery service narrows the trial-vs-real gap.
Sources and methodology
Real-world weight loss data synthesized from: Gleason et al, “Real-world semaglutide outcomes in commercially-insured adults” (Truveta 2024 publication, n=7,881); Epic Cosmos GLP-1 Outcomes Dashboard 2024 (n=24,400 Ozempic patients); Truveta tirzepatide cohort analysis 2024 (n=3,624 Zepbound patients); Komodo Health Mounjaro real-world evidence study 2024 (n=18,200). Clinical trial data from Wilding et al (STEP 1, NEJM 2021), Jastreboff et al (SURMOUNT 1, NEJM 2022), Pratley et al (SUSTAIN 7, Lancet 2018), Ludvik et al (SURPASS 3, Lancet 2021). Adherence and discontinuation data from IQVIA real-world drug utilization reports 2024.
How to cite this report
For journalists and researchers: cite as “MealFan, GLP-1 Real-World Weight Loss Data 2026, 12, 2026” with a link to this page. All data tables are free to embed with attribution.
