Semaglutide and tirzepatide are the two dominant GLP-1 receptor agonist molecules on the market in 2026 — sold under four primary brand names that confuse nearly every new patient. The core distinction is simple: Ozempic and Wegovy are the same molecule (semaglutide) at different doses for different FDA indications; Mounjaro and Zepbound are the same molecule (tirzepatide) at different dose ranges for different FDA indications. Tirzepatide is a dual GIP/GLP-1 agonist — it activates both the GIP receptor (glucose-dependent insulinotropic polypeptide) and the GLP-1 receptor simultaneously, which appears to produce greater weight loss than GLP-1-only agonism at equivalent tolerability. The clinical trial data shows meaningful and consistent separation in weight loss outcomes between the two drugs at their highest approved doses.
| Drug | Molecule | Mechanism | FDA Indication | Dose Range | Phase-up Schedule | Avg Weight Loss (trial) |
|---|---|---|---|---|---|---|
| Ozempic | Semaglutide | GLP-1 RA | T2D (glycemic control) | 0.25mg → 0.5mg → 1mg → 2mg weekly | 0.25mg × 4wks → 0.5mg; escalate PRN | −5–7kg at 1mg; −9kg at 2mg (SUSTAIN trials) |
| Wegovy | Semaglutide | GLP-1 RA | Chronic weight management (BMI ≥30, or ≥27 + comorbidity) | 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg weekly | 4 weeks per step; 16 weeks to maintenance dose | −14.9% (STEP 1); −12.4% (STEP 5 at 2 years) |
| Mounjaro | Tirzepatide | Dual GIP + GLP-1 RA | T2D (glycemic control) | 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg weekly | 2.5mg × 4wks → 5mg; escalate every 4wks as tolerated | −11.2 to −14.1 kg (SURPASS-1 through -5) |
| Zepbound | Tirzepatide | Dual GIP + GLP-1 RA | Chronic weight management (BMI ≥30, or ≥27 + comorbidity); also OSA (2025 FDA approval) | 2.5mg → 5mg → 10mg → 15mg weekly | Same as Mounjaro; 10mg and 15mg are typical maintenance doses for weight | −22.5% at 15mg (SURMOUNT-1); −20.2% (SURMOUNT-5) |
| Situation | Recommended Drug | Reasoning |
|---|---|---|
| Type 2 diabetes + want weight loss, good insurance for diabetes drugs | Mounjaro (tirzepatide) or Ozempic (semaglutide) | Both FDA-approved for T2D; Mounjaro shows greater weight loss and A1C reduction; covered under diabetes indication which has broader insurance coverage than obesity |
| Obesity without diabetes, insurance covers Wegovy/Zepbound | Zepbound (tirzepatide 15mg) | SURMOUNT-5 shows 47% greater weight loss than Wegovy at comparable doses; both are obesity-indication drugs |
| Obesity without diabetes, self-pay | Zepbound via Eli Lilly's self-pay program (~$550/mo) or Wegovy's $25/mo uninsured program | Access programs meaningfully reduce cost; Zepbound self-pay price is lower than Wegovy list |
| Prior poor GI tolerance of GLP-1 | Consider slower titration of semaglutide vs switching to tirzepatide | GI side effect profiles are similar; tirzepatide's GIP component may slightly blunt GI effects vs pure GLP-1; slower titration is the most effective intervention for both |
| Cardiovascular risk reduction as primary goal | Semaglutide (SELECT trial: −20% MACE in non-diabetic obese patients) | SELECT (2023, NEJM, N=17,604) is the largest CV outcomes trial of a GLP-1 in non-diabetic patients; tirzepatide CVOT data expected 2025–2026 |
| Obstructive sleep apnea treatment | Zepbound (FDA approved for OSA in 2025) | SURMOUNT-OSA trial: tirzepatide reduced AHI (apnea-hypopnea index) by ~60% — approved as adjunct to CPAP or as standalone in mild-moderate OSA |
Ozempic vs Wegovy (semaglutide): a prescriber can technically prescribe Ozempic pens and use them at Wegovy doses (2.4mg), and some do off-label when insurance covers Ozempic (diabetes) but not Wegovy (obesity). The pharmacokinetics are identical — it's the same drug. Ozempic pens are available in 0.5mg, 1mg, and 2mg delivery options. The 2.4mg Wegovy dose requires the Wegovy-specific pen format. Off-label dosing at 2.4mg via Ozempic pens involves drawing and administering a partial pen or using multiple injections — complex and not recommended without physician guidance.
Mounjaro vs Zepbound (tirzepatide): identical molecule, same doses (both go up to 15mg/week), but Mounjaro is labeled for T2D and Zepbound for obesity + OSA. Some prescribers prescribe Mounjaro off-label for obesity when insurance covers diabetes drugs more generously — same outcome, lower cost. The pens are identical in format.
Compounded versions: during shortage periods, FDA-registered 503B compounding pharmacies legally produced semaglutide and tirzepatide base compounds (not salts) at substantially lower prices ($100–300/month). The FDA removed semaglutide from its shortage list in October 2024, triggering a phase-out of compounding that was contested in court. Tirzepatide compound status has fluctuated. If you're using or considering compounded GLP-1 drugs, verify current legal status and only use FDA-registered 503B compounders — not telehealth programs that compound through unregistered pharmacies.
What happens when you stop: STEP 4 (2021) and SURMOUNT-4 (2023): both semaglutide and tirzepatide show weight regain of ~50–65% of lost weight within 12 months of discontinuation; the drugs suppress appetite via CNS GLP-1 receptors — the drive to eat returns when the drug stops; this has reframed GLP-1 agonists as chronic disease medications analogous to antihypertensives — not a course of treatment but an ongoing therapy for a chronic condition (obesity).