Last updated: May 18, 2026
Side-by-side at a glance
| Semaglutide | Tirzepatide | |
|---|---|---|
| Brand names | Ozempic (T2D), Wegovy (obesity), Rybelsus (oral) | Mounjaro (T2D), Zepbound (obesity) |
| Mechanism | GLP-1 receptor agonist | Dual GLP-1 + GIP receptor agonist |
| Half-life | ~1 week (165 hours) | ~5 days (~120 hours) |
| Max obesity dose | 2.4 mg/week | 15 mg/week |
| Trial weight loss (72wk) | ~15% (STEP 1) | ~21% (SURMOUNT-1) |
| HbA1c reduction | ~1.5-1.8pp | ~1.9-2.4pp |
How they work — the mechanism difference
Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist. It mimics endogenous GLP-1, an incretin hormone released by L-cells in the small intestine after eating. The molecular structure includes a C18 fatty acid chain that binds albumin to extend half-life from ~2 minutes (native GLP-1) to ~1 week.
Tirzepatide is a “twincretin” — a single peptide that activates both the GLP-1 receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor. The dual mechanism produces additive effects on glucose control and weight. This single difference — adding GIP receptor activity to GLP-1 — is the source of nearly every clinical distinction between the two drugs.
Efficacy: weight loss
STEP 1 (semaglutide 2.4mg, 68 weeks): Mean weight reduction 14.9%. 50% achieved ≥15% weight loss.
SURMOUNT-1 (tirzepatide 15mg, 72 weeks): Mean weight reduction 20.9%. 57% achieved ≥20% weight loss at 15mg.
Practical interpretation: for non-diabetic obesity, tirzepatide produces ~5-6 percentage points more weight loss than semaglutide at maximally titrated doses.
Efficacy: glycemic control
SURPASS-2 head-to-head (T2D, 40 weeks): Tirzepatide 5/10/15mg HbA1c reductions: -2.01 / -2.24 / -2.30 percentage points vs semaglutide 1mg: -1.86 percentage points. Tirzepatide produced superior HbA1c reduction at all three doses.
Side effects: where they’re similar, where they differ
Both drugs share the GLP-1 side-effect profile, dominated by gastrointestinal symptoms during titration: nausea (40-45% in early titration), vomiting, diarrhea, constipation, decreased appetite. Tirzepatide tends to produce slightly more GI symptoms in early titration but the overall tolerability profile is comparable.
Both share boxed warnings: thyroid C-cell tumors (medullary thyroid carcinoma), pancreatitis, gallbladder disease, hypoglycemia when combined with insulin or sulfonylureas.
Cost and insurance (US, 2026)
Wegovy/Ozempic: roughly $1,300-1,500/month list price. Zepbound/Mounjaro: roughly $1,000-1,300/month; Eli Lilly offers a self-pay program (LillyDirect) at $399/month for lower doses.
Which is better?
- Maximum weight loss potential → tirzepatide
- Established cardiovascular outcomes data → semaglutide (SELECT trial: 20% reduction in MACE)
- First time on a GLP-1 → semaglutide at lower starting doses
- Type 2 diabetes → tirzepatide modestly outperforms
Is tirzepatide stronger than semaglutide?<br />
For weight loss and glycemic control, yes — head-to-head trials show larger average reductions in body weight and HbA1c. The dual GLP-1/GIP mechanism accounts for the difference.
Can you switch from semaglutide to tirzepatide?<br />
Yes, this is common in practice. Most clinicians start tirzepatide at the standard 2.5mg starting dose even when switching, then titrate.
Do you regain weight after stopping?<br />
STEP 4 and SURMOUNT-4 showed substantial weight regain — typically two-thirds of lost weight regained within 12 months. These are long-term therapies.
Which has better long-term safety data?<br />
Semaglutide has more — approved for type 2 diabetes since 2017 vs 2022 for tirzepatide. Both have generally favorable profiles to date.