Sources & bibliography
Every score and guide on this site is built from primary sources, randomized trials, FDA labeling, and regulator or professional guidance, not press releases. Here are all 19 of them in one place, with each study’s manufacturer funding disclosed and a link wherever the source is public.
Randomized clinical trials
The efficacy and maintenance numbers we quote come from these head-to-head and placebo-controlled trials of the FDA-approved drugs. Every one was funded by the drug’s manufacturer, and we say so each time.
- STEP 1. Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. New England Journal of Medicine, 2021 (NEJMoa2032183). 1,961 adults, 68 weeks; mean weight change −14.9% vs −2.4% placebo.
- OASIS 4. Oral semaglutide 25 mg for chronic weight management (phase 3, 307 adults without diabetes, 64 weeks on treatment): 16.6% mean weight loss with full adherence vs 2.7% placebo, and 13.6% vs 2.2% on the treatment-policy estimand. The basis for the FDA approval of oral Wegovy in December 2025.
- SURMOUNT-1. Jastreboff AM et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine, 2022 (NEJMoa2206038). 72 weeks; up to −20.9% (treatment-regimen estimand) vs −3.1% placebo.
- SURMOUNT-5: tirzepatide vs. semaglutide, head-to-head. New England Journal of Medicine, 2025 (NEJMoa2416394). 751 adults, 72 weeks, maximum tolerated doses; tirzepatide −20.2% vs semaglutide −13.7%.
- SELECT: semaglutide 2.4 mg cardiovascular outcomes trial. New England Journal of Medicine, 2023 (NEJMoa2307563). Established CVD + overweight/obesity without diabetes; ~20% reduction in major adverse cardiovascular events.
- STEP 4. Rubino D et al. Effect of Continued Weekly Subcutaneous Semaglutide vs Placebo on Weight Loss Maintenance. JAMA, 2021;325(14):1414–1425. Continuing the drug added −7.9% over weeks 20–68 vs +6.9% regain on placebo.
- SURMOUNT-4. Aronne LJ et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity. JAMA, 2024;331(1):38–48. Continuing the drug added −5.5% vs +14.0% regain on placebo.
- STEP 1 trial extension. Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022;24(8):1553–1564 (PMID 35441470). One year after stopping, participants regained about two-thirds of the weight lost.
Real-world evidence
Trials run under ideal conditions. This cohort shows what happens in ordinary clinical care, including when people stop early.
- Gasoyan H et al. Changes in weight and glycemic control following obesity treatment with semaglutide or tirzepatide by discontinuation status. Obesity, 2025. Cleveland Clinic electronic-health-record cohort of 7,881 adults; one-year weight change −11.9% for those who stayed on treatment vs −3.6% for early discontinuers.
FDA drug labeling
The prescribing information is the regulatory source of truth for dosing schedules and adverse-reaction rates. We cite it for both approved drugs.
- FDA Prescribing Information, Wegovy (semaglutide): dosing schedule, adverse reactions (adult trials), warnings and precautions.
- FDA Prescribing Information, Zepbound (tirzepatide): dosing schedule, adverse reactions, warnings and precautions.
FDA safety & compounding communications
Our compounded-GLP-1 coverage leans on the FDA’s own safety communications and the end of the shortage-era compounding window.
- FDA, FDA’s Concerns with Unapproved GLP-1 Drugs Used for Weight Loss: compounded drugs do not undergo FDA premarket review for safety, quality, or effectiveness.
- FDA, FDA alerts health care providers, compounders and patients of dosing errors associated with compounded injectable semaglutide products (reports include a patient who self-administered a dose 10× higher than intended).
- FDA drug-shortage determinations: tirzepatide resolved December 2024; semaglutide resolved February 21, 2025 (503A compounding of copies ended April 22, 2025; 503B ended May 22, 2025).
- FDA, FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on the 503B Bulks List (announced April 30, 2026; Federal Register 2026-08552).
Professional & regulatory guidance
Safety questions beyond the label (surgery, eye risk, side-effect management) are sourced to professional societies and regulators, not to marketing.
- American Society of Anesthesiologists: consensus guidance on preoperative GLP-1 management (2023) and the multi-society update (October 2024).
- European Medicines Agency PRAC recommendation on semaglutide and NAION (June 2025); WHO medical product alert (June 2025).
- University of Illinois Chicago Drug Information Group: safety concerns with compounded GLP-1 receptor agonists (August 2025).
- Multidisciplinary expert consensus on managing GI adverse events with GLP-1 receptor agonists (PMC9821052); “Do no harm: managing nausea and vomiting in GLP-1 therapies” (PMC12992036).
Community reports
Where our guides quote patterns from patient communities (“65 of 184 comments reported minimal side effects”), every figure comes from a dated, documented count over named threads. We paraphrase patterns and never reprint usernames or individual quotes. The full method, and the thread list behind each article, lives in the methodology.
Each article also lists the exact sources behind its specific claims in its own “Sources & methodology” section. For how these sources turn into a score, see our 31-point methodology. Spot an error? We log every correction publicly. Tell us.