Semaglutide and tirzepatide are both highly effective GLP-1 medications for weight loss — but they are not identical. Understanding the differences helps you and your physician make the best choice for your situation.
How They Work Differently
Semaglutide is a GLP-1 receptor agonist. It works by mimicking GLP-1, a hormone that: - Slows gastric emptying (you feel full longer) - Suppresses appetite signals in the brain - Stimulates insulin secretion in response to meals - Reduces glucagon (which raises blood sugar)
Tirzepatide is a dual GLP-1/GIP receptor agonist. It does everything semaglutide does, plus activates GIP receptors. GIP (glucose-dependent insulinotropic polypeptide) works synergistically with GLP-1 in ways that appear to produce greater fat loss and better metabolic effects.
The dual mechanism is why tirzepatide produces larger average weight loss than semaglutide in clinical trials.
Head-to-Head Trial Data
The SURMOUNT-1 trial (tirzepatide for weight loss) and STEP-1 trial (semaglutide for weight loss) were not head-to-head, but they used similar methodologies:
Semaglutide 2.4mg (STEP-1, 68 weeks): - Average weight loss: 14.9% of body weight - ≥5% weight loss: 86% of participants - ≥15% weight loss: 32% of participants - ≥20% weight loss: 14% of participants
Tirzepatide 15mg (SURMOUNT-1, 72 weeks): - Average weight loss: 20.9% of body weight - ≥5% weight loss: 91% of participants - ≥15% weight loss: 57% of participants - ≥20% weight loss: 36% of participants
There is also a direct head-to-head trial: SURMOUNT-5 (published late 2024), which showed tirzepatide produced approximately 47% more weight loss than semaglutide in patients with obesity.
The evidence is clear: tirzepatide produces greater average weight loss.
Side Effect Comparison
Both medications share similar GI side effects. The differences are modest.
Common to both: - Nausea (most common, especially early weeks) - Vomiting - Diarrhea or constipation - Decreased appetite - Injection site reactions
Nausea comparison: - Semaglutide: ~44% of patients report nausea (STEP-1) - Tirzepatide: ~30–40% of patients report nausea (SURMOUNT-1, dose-dependent)
Some patients report tirzepatide causes less nausea than semaglutide at comparable doses, potentially because the GIP component partially counteracts GLP-1-induced nausea — but this isn't consistent across all patients.
Who Does Better on Each?
Consider semaglutide if: - You want a well-established medication with 5+ years of real-world data at scale - Cost is a constraint (both are offered as compounded, but pricing can vary) - Your weight loss goal is moderate (20–40 lbs) - Your physician has more experience prescribing it
Consider tirzepatide if: - You have significant weight to lose (50+ lbs) - You have type 2 diabetes or insulin resistance (tirzepatide has a significant glycemic advantage) - You want the maximum efficacy option - You've tried GLP-1 monotherapy before with limited results
Compounded Availability
Both medications are available as compounded injections from FDA-registered 503B pharmacies. Compounded versions are significantly less expensive than brand-name Ozempic, Wegovy, or Mounjaro — making access possible for patients who can't afford or access the branded versions.
Marrow offers both compounded semaglutide and tirzepatide. Your intake assessment helps determine which is the right starting point.
The Bottom Line
If your primary goal is maximum weight loss and you don't have a strong reason to prefer semaglutide, tirzepatide is the stronger choice based on current trial data. The dual mechanism produces meaningfully greater weight loss in clinical trials and real-world data.
That said, the best medication is the one you'll actually take consistently and tolerate well. Individual response varies. Some patients do better on semaglutide despite tirzepatide's statistical advantage.
Talk to your Marrow physician — they'll factor in your goals, medical history, and individual circumstances before recommending a protocol.
Frequently Asked Questions
Is tirzepatide stronger than semaglutide?
Yes, on average. Clinical trials show tirzepatide produces approximately 20–21% body weight loss vs. 14–15% for semaglutide. The SURMOUNT-5 head-to-head trial showed tirzepatide produced about 47% more weight loss than semaglutide. Individual results vary.
Which has fewer side effects — semaglutide or tirzepatide?
They have very similar side effect profiles. Both primarily cause GI symptoms (nausea, constipation, occasional vomiting). Some data suggests tirzepatide may cause slightly less nausea, but this isn't consistent across all patients. Individual tolerance varies significantly.
Can I switch from semaglutide to tirzepatide?
Yes. Switching between GLP-1 medications is common when a patient doesn't achieve desired results on one. There's typically a transition period where dosing is adjusted. Your physician will guide the timing and starting dose for the new medication.
Is compounded tirzepatide the same as Mounjaro?
Compounded tirzepatide contains the same active ingredient (tirzepatide) as Mounjaro and Zepbound. Compounded versions are manufactured at FDA-registered 503B pharmacies, not by Eli Lilly. The active molecule is identical; excipients and formulation may differ slightly.
Get our free Body Composition Guide
Protein protocols, workout structure, sleep optimization, and the supplement stack that actually works.
Get our free Body Composition Guide →
