Semaglutide vs Tirzepatide: A Complete Comparison

What Are GLP-1 Receptor Agonists?#

GLP-1 (glucagon-like peptide-1) receptor agonists are a class of medications that mimic the hormone GLP-1, which is naturally released by the gut after eating. These compounds slow gastric emptying, reduce appetite, increase insulin secretion, and suppress glucagon — creating a powerful hormonal environment for weight loss and blood sugar control. Both semaglutide and tirzepatide belong to this class, though they differ significantly in how they work and how effective they are.

How Semaglutide Works#

Semaglutide (brand names: Ozempic, Wegovy) is a GLP-1 receptor agonist with approximately 94% homology to human GLP-1. Injected weekly, it reduces appetite by acting on the hypothalamus, slows gastric emptying, and improves glycemic control. The STEP clinical trial program showed semaglutide 2.4mg weekly produced an average of 14.9% body weight reduction over 68 weeks in non-diabetic adults.

Average weight loss with semaglutide 2.4mg: ~15% body weight over 68 weeks (STEP 1 trial)

How Tirzepatide Works#

Tirzepatide (brand names: Mounjaro for diabetes, Zepbound for obesity) is a dual GIP/GLP-1 receptor agonist — a key distinction from semaglutide. GIP (glucose-dependent insulinotropic polypeptide) is a second incretin hormone that works through a complementary pathway. By activating both receptors simultaneously, tirzepatide produces additive effects on appetite suppression and metabolic function. The SURMOUNT-1 trial showed tirzepatide 15mg produced average weight loss of 20.9% over 72 weeks.

Average weight loss with tirzepatide 15mg: ~21% body weight over 72 weeks (SURMOUNT-1 trial)

Dosing Compared#

Semaglutide is started at 0.25mg weekly and escalated over 16-20 weeks to the 2.4mg maintenance dose (Wegovy protocol). Tirzepatide starts at 2.5mg weekly and escalates in 2.5mg increments every 4 weeks, reaching a maximum of 15mg. Compounded versions of both are available through telehealth providers at significantly lower cost than brand-name versions. Escalation is designed to minimise GI side effects — skipping the titration schedule increases the risk of nausea and vomiting.

Side Effects#

Both compounds share a similar GI side effect profile: nausea, vomiting, diarrhea, and constipation are most common, particularly during dose escalation. These typically subside as the body adjusts. Tirzepatide side effects are reported at slightly lower rates in trials despite its superior weight loss outcomes. Both carry a precautionary warning regarding thyroid C-cell tumors based on rodent studies. Both are contraindicated in patients with a personal or family history of medullary thyroid carcinoma.

Head-to-Head: Which Is More Effective?#

Tirzepatide produces greater weight loss than semaglutide. The SURMOUNT-5 trial directly compared the two and found tirzepatide led to significantly greater mean weight loss (-20.2% vs -13.7% for semaglutide 2.4mg at 72 weeks). This ~7 percentage point gap is clinically meaningful. However, semaglutide has a longer track record and more real-world safety data. For patients who respond well to semaglutide and tolerate it, switching may not be necessary.

Head-to-head (SURMOUNT-5): Tirzepatide -20.2% vs Semaglutide -13.7% at 72 weeks

Liraglutide vs Semaglutide#

Liraglutide (Saxenda) is an older GLP-1 agonist dosed daily rather than weekly. It produces average weight loss of 5-8% body weight — substantially less than weekly semaglutide or tirzepatide. The main advantage of liraglutide is its established long-term safety record and faster clearance if side effects are an issue. Most prescribers now start patients on semaglutide or tirzepatide rather than liraglutide due to superior efficacy and weekly dosing convenience.

Cost and Access#

Brand-name semaglutide (Wegovy) and tirzepatide (Zepbound) are expensive in the US without insurance — typically $900-$1,400/month. Compounded versions from 503B pharmacies are substantially cheaper ($100-$300/month) and widely available through telehealth platforms. Insurance coverage has improved but remains inconsistent. The compounding exemption has faced regulatory pressure from the FDA, so cost and availability may change. Both require a prescription.