Overview
Tirzepatide (Mounjaro/Zepbound) and semaglutide (Ozempic/Wegovy) are both GLP-1-based peptides for diabetes and weight management. The key difference: tirzepatide is a dual GIP/GLP-1 receptor agonist, while semaglutide targets only GLP-1. This dual mechanism may explain tirzepatide's superior weight loss in head-to-head trials.
Mechanism of Action Comparison
Semaglutide: Selective GLP-1 receptor agonist. Slows gastric emptying, enhances insulin secretion, suppresses glucagon, reduces appetite via hypothalamic signaling.
Tirzepatide: Dual GIP + GLP-1 receptor agonist. In addition to GLP-1 effects, GIP activation enhances fat mobilization and may improve insulin sensitivity through adipose tissue signaling. This dual pathway produces greater caloric deficit.
Half-Life and Dosing Frequency
• Semaglutide half-life: ~168 hours (7 days) → once weekly
• Tirzepatide half-life: ~120 hours (5 days) → once weekly
Both are dosed once weekly. Tirzepatide's shorter half-life means slightly faster washout if side effects occur.
Dose Escalation Schedules
Semaglutide (Wegovy): 0.25 mg → 0.5 mg → 1.0 mg → 1.7 mg → 2.4 mg (escalation every 4 weeks)
Tirzepatide (Mounjaro): 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg (escalation every 4 weeks)
Note the dose magnitudes differ significantly — tirzepatide is dosed in higher absolute milligrams.
Clinical Weight Loss Data
SURMOUNT-1 (tirzepatide, n=2,539): 15 mg arm achieved 22.5% mean weight loss vs. 3.1% placebo over 72 weeks.
STEP 1 (semaglutide, n=1,961): 2.4 mg arm achieved 14.9% mean weight loss vs. 2.4% placebo over 68 weeks.
In the head-to-head SURMOUNT-5 trial, tirzepatide 15 mg outperformed semaglutide 2.4 mg (20.2% vs. 13.7% weight loss).
Side Effect Profiles
Both share GI side effects (nausea, diarrhea, constipation, vomiting). Tirzepatide may cause slightly higher rates of diarrhea initially. Both carry FDA boxed warnings for thyroid C-cell tumors (observed in rodents, not confirmed in humans).
Serious but rare: pancreatitis, gallbladder disease, hypoglycemia (mainly when co-administered with insulin/sulfonylureas).
Which Should You Choose?
This depends on clinical context. Tirzepatide shows greater weight loss in trials and may be preferred when maximum weight reduction is the primary goal. Semaglutide has a longer track record, more published safety data, and cardiovascular outcome trial support (SELECT trial).
Always consult a healthcare provider for personalized guidance. Use our GLP-1 Dose Scheduler to generate your week-by-week injection schedule for either medication.