Tirzepatide vs semaglutide: the head-to-head, simplified

Semaglutide is a single-agonist GLP-1 receptor agonist. It mimics the effect of the body's own glucagon-like peptide-1 — slowing gastric emptying, enhancing glucose-dependent insulin secretion, and reducing appetite.

Tirzepatide is a dual agonist of both the GLP-1 receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor. The added GIP activity appears to contribute additional metabolic effect, including on energy expenditure, lipid handling, and possibly central appetite regulation. The result is a larger effect size in most outcomes that have been measured head-to-head.

In SURPASS-2 (Frías et al., NEJM 2021), tirzepatide 15 mg produced a mean HbA1c reduction of 2.30 percentage points vs 1.86 for semaglutide 1 mg in adults with type 2 diabetes — a roughly 0.45-point greater reduction at the highest doses. Mean weight loss was 11.2 kg with tirzepatide 15 mg vs 5.7 kg with semaglutide 1 mg.

In obesity-focused trials, SURMOUNT-1 (tirzepatide 15 mg) produced mean weight loss of 22.5% over 72 weeks vs STEP-1 (semaglutide 2.4 mg) at 14.9% over 68 weeks. The trials weren't direct head-to-head at obesity doses, but the effect-size differential is consistent with the SURPASS-2 head-to-head at diabetes doses.

Both drugs share the same major side-effect category — gastrointestinal symptoms, primarily nausea, diarrhea, vomiting, and constipation — predominantly during dose escalation. Discontinuation rates in trials are broadly similar (4–8% on either drug vs 2–3% on placebo).

Tirzepatide may produce slightly more pronounced GI symptoms at the highest doses, consistent with its larger effect size, though the head-to-head data are mixed. There is no clear differential in serious adverse events.

FDA-approved brand-name versions of both drugs list in similar ranges: Ozempic and Wegovy (semaglutide) at roughly $900–$1,350/month list before insurance; Mounjaro and Zepbound (tirzepatide) at $1,000–$1,200/month. Eli Lilly's LillyDirect cash-pay program offers reduced pricing on tirzepatide single-dose vials.

Compounded versions of both drugs are substantially less expensive — typically $145–$300/month for semaglutide and $185–$500/month for tirzepatide via legitimate telehealth programs. Compounded versions are not FDA-approved and are not the same as the brand-name drugs.

For pure weight-loss magnitude with no comorbid indication, tirzepatide has the larger effect size in trials and is the more probable first choice if cost permits. For patients with established cardiovascular disease and obesity, semaglutide 2.4 mg (Wegovy) is the only weight-loss drug with an FDA cardiovascular-risk-reduction indication, based on the SELECT trial.

For patients on a tight cash budget, the compounded semaglutide price floor is lower than compounded tirzepatide, though both are accessible through reputable telehealth programs. Insurance coverage varies meaningfully between the two, especially for the obesity indication.