How do semaglutide and tirzepatide compare?
| Feature | Semaglutide | Tirzepatide |
|---|---|---|
| Mechanism | Selective GLP-1 receptor agonist | Dual GIP + GLP-1 receptor agonist |
| Dosing frequency | Once weekly (subcutaneous injection) | Once weekly (subcutaneous injection) |
| Key trial | STEP 1 (~15% body-weight reduction over 68 weeks) | SURMOUNT-1 (~20–21% body-weight reduction over 72 weeks) |
| Common side effects | Nausea, vomiting, diarrhea, constipation | Similar GI profile; comparable tolerability |
| Key contraindications | MTC or MEN2 history, pregnancy | MTC or MEN2 history, pregnancy |
| Compounded availability | Yes — 503A pharmacy, valid Rx required | Yes — 503A pharmacy, valid Rx required |
What does “GLP-1” actually mean?
“GLP-1” is shorthand for a class of medications that activate the glucagon-like peptide-1 receptor, a receptor expressed in the brain, gut, and pancreas that mediates satiety signaling, gastric motility, and incretin-driven insulin modulation. The class name covers several distinct molecules with different receptor affinities, half-lives, and clinical profiles.
For weight management specifically, the two GLP-1 brands with the most robust published trial data are semaglutide (weekly injection) and tirzepatide (weekly injection). They are not interchangeable — they differ in mechanism, average trial outcomes, and tolerability profiles. Understanding the difference matters when you’re making a clinical decision.
How does semaglutide work?
Semaglutide is a GLP-1 receptor agonist with high selectivity for the GLP-1 receptor. Weekly subcutaneous injection produces sustained receptor activation, prolonged satiety signaling, and slowed gastric emptying. Its half-life of approximately one week makes once-weekly dosing practical.
The STEP 1 trial (published in the New England Journal of Medicine) documented average weight reduction of approximately 15% of body weight over 68 weeks at the 2.4 mg maintenance dose in adults with obesity but without diabetes. That trial used the branded formulation; compounded semaglutide contains the same active molecule but is not the same product and has not been independently studied at the same scale.
Common side effects in trials included nausea, vomiting, diarrhea, and constipation — most pronounced during the titration phase and generally reducing over time. Contraindications include personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.
How is tirzepatide different?
Tirzepatide takes a different approach. It is a dual agonist— it activates both the GLP-1 receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor simultaneously. GIP is a second incretin hormone that works alongside GLP-1 in appetite and energy homeostasis. Activating both receptors appears to produce additive or synergistic effects on weight reduction compared to GLP-1 activation alone.
The SURMOUNT-1 trial documented average weight reduction of approximately 20–21% of body weight over 72 weeksat the highest doses studied in adults with obesity without diabetes — meaningfully higher than the STEP 1 semaglutide outcomes, though these are different trials with different populations and cannot be directly compared. The SURPASS-2 head-to-head trial in patients with type 2 diabetes showed greater reductions in both weight and HbA1c with tirzepatide versus semaglutide at matched doses.
Tirzepatide carries similar GI side-effect and contraindication profiles to semaglutide. Dose titration follows a similar gradual escalation structure.
What does the compounded shortage pathway mean?
Branded semaglutide and tirzepatide have faced documented supply shortages. During shortage periods, the FDA’s compounding rules permit licensed 503A pharmacies to prepare compounded versions of those molecules for individual patients with valid prescriptions.
Compounded semaglutide and compounded tirzepatide are not branded products — they are not FDA-approved, and they are not manufactured by the original drug sponsors. But they contain the same active molecules, prepared by licensed pharmacies under 503Aoversight with a clinician’s prescription. This is the clinician-supervised path most patients take during constrained supply periods.
At PepScribe, every compounded GLP-1 is prepared by licensed 503A pharmacies in the USA. No hidden overseas supply chain. The 503A standard means patient-specific compounding under pharmacy oversight — not bulk manufacturing, not international sourcing, not gray-market supply.
How do clinicians choose between GLP-1 brands?
The choice between semaglutide and tirzepatide is not a consumer preference decision — it is a clinical one. Factors that influence the prescribing decision include:
- Health history: Prior GI conditions, thyroid history, pancreatitis history, and current medications all factor into which molecule is appropriate.
- Clinical goals:If significant weight reduction is the primary goal, tirzepatide’s trial data is stronger at higher doses. But individual response does not always mirror population averages.
- Formulary availability: Shortage status can affect which compounded option is accessible at a given time.
- Tolerability history: A patient who has tried one GLP-1 brand and had significant tolerability issues may respond differently to the other. Clinician-managed titration is the tool for managing this.
No article — including this one — substitutes for a clinician reviewing your specific situation. GLP-1 therapy is prescription medicine. Get the clinical consultation first.
Frequently asked questions
What is the key difference between semaglutide and tirzepatide?
Semaglutide is a GLP-1 receptor agonist. Tirzepatide is a dual GIP/GLP-1 receptor agonist — it activates both the GIP and GLP-1 incretin pathways simultaneously. Published trials have reported greater average weight reduction with tirzepatide, though individual response differs based on clinical factors.
Which GLP-1 brand is best for weight management?
There is no universal "best." The choice between semaglutide and tirzepatide depends on your health history, tolerance profile, current formulary availability, and clinical goals. A licensed clinician makes that determination after reviewing your intake — not a product comparison page.
Are compounded GLP-1s the same as branded GLP-1 drugs?
Compounded semaglutide and tirzepatide contain the same active molecules as their branded counterparts but are not the same products. They are not FDA-approved; they are prepared by licensed 503A compounding pharmacies under shortage exemption pathways for individual patients with valid prescriptions.
How often are GLP-1 injections administered?
Most clinician-prescribed GLP-1 protocols use weekly subcutaneous injections. Dosing starts low and is titrated upward over several weeks to improve tolerability. Specific dosing schedules are set by the prescribing clinician based on individual response.
Do GLP-1 medications require a prescription?
Yes. All GLP-1 receptor agonists — branded or compounded — require a prescription from a licensed clinician. There is no legal OTC version of semaglutide or tirzepatide.