The two GLP-1 heavyweights, head to head. Same family, different firepower.
Bottom line: The SURMOUNT-5 trial settled this: tirzepatide produced 20.2% weight loss vs semaglutide's 13.7% over 72 weeks , a 47% larger result. The dual GLP-1/GIP mechanism isn't just a marketing angle, it's a meaningfully different mechanism that shows up in the data. That said, semaglutide has one thing tirz doesn't: a dedicated cardiovascular outcomes trial (SELECT) proving it cuts MACE in people with obesity. Tirz's cardiovascular data is coming but thinner. If max weight loss is the goal, tirz wins. If you want the deepest safety track record or an oral option, sema is the rational choice.
| Semaglutide | Tirzepatide | |
|---|---|---|
| Category | GLP-1 receptor agonist | Dual GLP-1/GIP receptor agonist |
| Mechanism | Mimics GLP-1 to suppress appetite and slow gastric emptying. One receptor, one signal. | Hits both GLP-1 and GIP receptors simultaneously. GIP may amplify satiety and reduce nausea; the combination outperforms either alone. |
| Standard dose range | 0.25mg → 2.4mg weekly (injection); 3mg → 14mg daily (oral Rybelsus) | 2.5mg → 15mg weekly (injection only) |
| Injection frequency | Once weekly (injection) or once daily (oral) | Once weekly (injection) |
| Weight loss , best trial result | 14.9% at 68 weeks (STEP 1, 2.4mg); 20.7% at 72 weeks with investigational 7.2mg dose (STEP UP trial) | 20.9% at 72 weeks (SURMOUNT-1, 15mg); 22.5% in patients with highest efficacy |
| Head-to-head result | −13.7% at 72 weeks (SURMOUNT-5) | −20.2% at 72 weeks (SURMOUNT-5). Tirz won by 6.5 percentage points in the only direct trial. |
| Top side effects | Nausea (44%), diarrhea (30%), constipation (24%), vomiting (24%). GI events peak at each dose increase. | Nausea (31%), diarrhea (23%), constipation (18%), vomiting (12%). Lower discontinuation due to GI events in head-to-head (2.7% vs 5.6%). |
| Evidence tier | Tier 1 , multiple Phase 3 trials, FDA-approved 2021, dedicated cardiovascular CVOT (SELECT) | Tier 1 , Phase 3 complete, FDA-approved 2022, cardiovascular CVOT ongoing |
| FDA approval | Ozempic (T2D, 2017), Wegovy (obesity, 2021), Rybelsus (oral T2D, 2019) | Mounjaro (T2D, 2022), Zepbound (obesity, 2023) |
| Compounding status (2026) | FDA shortage resolved 2025. 503B pharmacy compounding largely ended. 503A patient-specific compounding still limited. Availability has tightened significantly. | Same situation. Shortage resolved Feb 2025. Broad compounding effectively ended. Some 503A telehealth providers still operating in a gray area. |
| Approximate monthly cost | Branded Wegovy ~$1,349/mo. Compounded (where available) ~$150–300/mo. | Branded Zepbound ~$1,086/mo. Compounded (where available) ~$200–400/mo. |
| Cardiovascular outcomes | SELECT trial: 20% MACE reduction in obese patients with CVD, no diabetes. First GLP-1 with dedicated obesity CVOT. | No dedicated cardiovascular CVOT for obesity yet. Real-world data mixed , some showing similar benefit, others showing sema edge in CV events. |
tierA: Tier 1
tierB: Tier 1
summary: Both drugs have completed large Phase 3 programs, FDA approval for diabetes and obesity, and millions of real-world patients. Semaglutide has more total years of data and a dedicated cardiovascular outcomes trial. Tirzepatide has the first direct head-to-head trial, which it won convincingly.
trials: [{"name":"STEP 1 (semaglutide)","pmid":"33567185","result":"14.9% mean body weight loss vs 2.4% placebo at 68 weeks (n=1,961)","citation":"Wilding JPH et al. N Engl J Med. 2021"},{"name":"STEP 5 (semaglutide, 2-year)","pmid":"36216945","result":"15.2% mean weight loss at 104 weeks vs 2.6% placebo (n=304)","citation":"Garvey WT et al. Nat Med. 2022"},{"name":"SELECT (semaglutide cardiovascular)","pmid":"37952131","result":"20% reduction in MACE in patients with obesity + CVD, no diabetes (n=17,604)","citation":"Lincoff AM et al. N Engl J Med. 2023"},{"name":"SURMOUNT-1 (tirzepatide)","pmid":"35658024","result":"20.9% mean weight loss at 15mg vs 3.1% placebo gain at 72 weeks (n=2,539)","citation":"Jastreboff AM et al. N Engl J Med. 2022"},{"name":"SURPASS-2 (head-to-head in T2D)","pmid":"34170647","result":"Tirzepatide 15mg reduced A1C by 2.46% vs semaglutide 1mg at 1.86%; weight loss 12.4 kg vs 6.2 kg (n=1,879)","citation":"Frías JP et al. N Engl J Med. 2021"},{"name":"SURMOUNT-5 (head-to-head in obesity, Phase IIIb)","pmid":"40353578","result":"Tirzepatide −20.2% vs semaglutide −13.7% at 72 weeks (p<0.001); GI discontinuation lower with tirz (2.7% vs 5.6%) (n=751)","citation":"Jastreboff AM et al. N Engl J Med. 2025"}]
{"applies":false,"name":"You don't stack these , you switch","intro":"Semaglutide and tirzepatide are not stacked together. They act on overlapping receptors and the combination would amplify side effects without adding meaningful benefit. People don't use both at once.","phases":[],"note":"The real 'stack' question here is sequencing: some people start on semaglutide (more widely available, often cheaper or insured) and switch to tirzepatide if they plateau or want stronger results. Others go straight to tirzepatide. If you want to add something to either, tesamorelin is sometimes used for targeted visceral fat reduction alongside a GLP-1 agonist."}
It's real. SURMOUNT-5 was a direct head-to-head RCT with 751 people , tirzepatide produced 20.2% weight loss vs semaglutide's 13.7% over the same 72 weeks. That's not a small difference, and it's consistent with what meta-analyses of indirect comparisons have shown. The dual GLP-1/GIP mechanism hits appetite from two angles, which appears to produce meaningfully stronger suppression for most people.
A few real reasons: semaglutide has an oral pill form (Rybelsus/compounded oral) for people who won't inject. It has more years of safety data. The SELECT cardiovascular outcomes trial , which is huge , was done on semaglutide, not tirzepatide. Some insurers cover Wegovy but not Zepbound. And in some markets, sema is simply more available. It's not the 'inferior' drug, it's the 'different trade-offs' drug.
Switching is a legitimate strategy that many clinicians use. If you've been on sema at a stable dose for 3+ months and weight loss has stalled, tirzepatide's different mechanism might restart progress. Most people who switch report the transition works , though you'll restart titration from the lowest tirz dose to manage GI tolerance. This isn't something to do impulsively; give sema a real chance at therapeutic dose first.
Tirzepatide tends to have fewer GI side effects in practice. SURMOUNT-5 found only 2.7% of tirz patients stopped due to GI events vs 5.6% of sema patients. The working theory is that the GIP receptor activation actually blunts nausea. That said, individual variation is large , some people tolerate sema perfectly and get wrecked by tirz. Slow titration matters more than drug choice.
No. These drugs act on overlapping receptor systems and are used as alternatives to each other, not in combination. Stacking them would multiply GI side effects and risks without adding meaningful benefit. Pick one.
Some lean mass loss is expected with any significant weight loss , that's just physiology. Semaglutide trials showed roughly 39% of weight lost was lean mass; tirzepatide showed ~25% in trial data, but a 2026 real-world analysis (medRxiv preprint) actually found greater lean body mass loss with tirz at every timepoint. Either way, the answer is the same: eat 1.2–1.6g of protein per kilogram of bodyweight and do resistance training. That's the only proven way to shift the fat-to-muscle ratio of your weight loss.
Barely, and it's complicated. The FDA resolved both drug shortages in 2025, which ended the legal basis for most pharmacy compounding. 503B bulk compounding was largely shut down. Some 503A pharmacies still compound patient-specific prescriptions under a narrower exception. The space changed fast , check your provider's current status and jurisdiction. Don't assume a supplier that was legal in 2024 is still operating legally.
Weight comes back. The STEP 1 extension study followed people for a year after stopping semaglutide and found they regained about two-thirds of lost weight. Tirz data shows similar patterns. These are not finish-line drugs , they work while you take them, and the mechanism stops when you stop. That's the honest framing before you start either one.
These statements have not been evaluated by the FDA. This content is for educational purposes only. Consult a healthcare professional before starting any protocol. vialprep sells injection supplies, not compounds.
