Tirzepatide is a dual GIP and GLP-1 receptor agonist: it activates two separate hormone receptors, GIP and GLP-1, rather than the single GLP-1 receptor semaglutide activates on its own. That second receptor is the leading mechanistic explanation for why tirzepatide produced more weight loss than semaglutide in the only randomised trial that has ever compared them directly, SURMOUNT-5: 20.2% mean weight loss at 72 weeks against semaglutide’s 13.7% (Aronne LJ, Horn DB, le Roux CW, Ho W, et al., New England Journal of Medicine, 3 July 2025, DOI 10.1056/NEJMoa2416394). That trial was open-label and funded by Eli Lilly, the company that makes tirzepatide, two facts worth weighing alongside the result rather than a reason to dismiss it.
Below: what the GIP and GLP-1 receptors actually do in the body, the head-to-head trial’s design and numbers with confidence intervals, what tirzepatide is sold as and what it is approved for, what its side effects look like and when they show up, who has a specific reason to ask a prescriber about it and who doesn’t, and how to actually get it prescribed today.
Key takeaways
What kind of drug is tirzepatide?
Tirzepatide is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone receptors rather than the one that semaglutide activates. It is sold as Mounjaro for type 2 diabetes and Zepbound for weight loss, both FDA-approved.
Does tirzepatide work better than semaglutide?
In the one randomised trial that compared them directly, yes: tirzepatide produced 20.2% mean weight loss at 72 weeks against semaglutide’s 13.7% (Aronne LJ, Horn DB, le Roux CW, Ho W, et al., NEJM, 2025). That trial, SURMOUNT-5, was open-label and funded by Eli Lilly, tirzepatide’s manufacturer.
What are tirzepatide’s most common side effects?
Gastrointestinal, in both the tirzepatide and semaglutide arms of SURMOUNT-5: mostly mild to moderate, occurring primarily during dose escalation. No incidence figures broken out by specific symptom are published in the source this page draws from.
Is Mounjaro the same drug as tirzepatide?
Yes. Tirzepatide is the active medication; Mounjaro is its FDA-approved brand name for type 2 diabetes, and Zepbound is its FDA-approved brand name for weight loss.
Can you buy tirzepatide without a prescription?
No. Tirzepatide requires a licensed prescriber’s evaluation before it can be started. The providers this page links to prescribe compounded tirzepatide after that evaluation, not without one.
Is tirzepatide the same as retatrutide?
No. Tirzepatide activates two receptors, GIP and GLP-1. Retatrutide activates a third, glucagon, on top of those two, which is why it is described as a triple agonist. Retatrutide is investigational and cannot legally be prescribed; tirzepatide is FDA-approved.
What “dual GIP and GLP-1 receptor agonist” actually means
Tirzepatide activates two separate hormone receptors: GLP-1 and GIP. The GLP-1 receptor is the same one semaglutide activates on its own: stimulating it slows stomach emptying, which keeps food in the stomach longer and extends the feeling of fullness, while also acting on appetite-signaling pathways in the brain. GIP, the second receptor tirzepatide adds, works through a separate pathway involved in insulin response and, current research suggests, its own effect on appetite. Activating both receptors at once, rather than GLP-1 alone, is the mechanistic explanation researchers point to for tirzepatide’s stronger measured result against semaglutide, though the trial that produced that result was designed to measure the outcome, not to isolate exactly how much each receptor contributed on its own.
Together, the two pathways are why tirzepatide curbs appetite and steadies blood sugar at the same time. Slower gastric emptying reduces how much a person wants to eat at a given meal, appetite-signaling in the brain reduces hunger between meals, and the GIP-linked insulin-response pathway helps the body manage blood sugar after eating. That combination is why tirzepatide, like semaglutide, is approved both for type 2 diabetes and for weight loss: the same two receptor pathways serve both indications, at different doses and in different patient populations, under two different brand names.
What the evidence shows: the only head-to-head trial
The dual-receptor mechanism is why tirzepatide beat semaglutide in the only randomised trial that has ever compared the two drugs directly, SURMOUNT-5. Aronne LJ, Horn DB, le Roux CW, Ho W and colleagues published it in the New England Journal of Medicine on 3 July 2025 (DOI 10.1056/NEJMoa2416394, PMID 40353578, registered as ClinicalTrials.gov NCT05822830). It was a phase 3b, open-label, controlled trial of 751 adults with obesity but without type 2 diabetes, randomised 1:1 to the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg), both once weekly by subcutaneous injection, for 72 weeks.
Tirzepatide produced a mean body weight change of −20.2% (95% CI −21.4 to −19.1) against semaglutide’s −13.7% (95% CI −14.9 to −12.6), P<0.001. Waist circumference moved the same direction: −18.4 cm (95% CI −19.6 to −17.2) on tirzepatide against −13.0 cm (95% CI −14.3 to −11.7) on semaglutide, also P<0.001. The trial also reports that tirzepatide participants were more likely to reach weight-loss reductions of at least 10%, 15%, 20% and 25% of body weight than semaglutide participants, stating that direction plainly without breaking out the exact share of participants at each threshold in the material this page draws from.
Two facts about SURMOUNT-5 belong next to that result, not buried below it. It was open-label: every participant and investigator knew which drug a given person was taking, which can shape adherence and how borderline side effects get recorded. And it was funded by Eli Lilly, the company that manufactures and sells tirzepatide as Mounjaro and Zepbound. Neither fact makes the −20.2% figure false or retroactively changes a pre-registered primary endpoint measured across 751 people. Both are reasons to weigh the number carefully rather than repeat it as a bare headline, which is exactly what this page is doing by stating them here.
| Tirzepatide | Semaglutide | |
|---|---|---|
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| Brand names | Mounjaro (type 2 diabetes), Zepbound (weight loss) | Ozempic (type 2 diabetes), Wegovy (weight loss) |
| FDA approval status | FDA-approved | FDA-approved |
| Dosing in SURMOUNT-5 | Maximum tolerated 10 or 15 mg, once weekly, subcutaneous | Maximum tolerated 1.7 or 2.4 mg, once weekly, subcutaneous |
| SURMOUNT-5 result at 72 weeks | −20.2% mean body weight change (95% CI −21.4 to −19.1) | −13.7% mean body weight change (95% CI −14.9 to −12.6) |
Side effects
Tirzepatide’s most common adverse events in SURMOUNT-5 were gastrointestinal, the same pattern reported in the semaglutide group in the same trial. Most were mild to moderate and occurred primarily during dose escalation, the period when the dose is being stepped up toward the maximum tolerated level rather than held steady (Aronne LJ, Horn DB, le Roux CW, Ho W, et al., NEJM, 2025). That pattern lines up with tirzepatide’s mechanism: both receptors it activates touch the digestive system, so a stronger version of that signal tends to be felt there first as the dose rises.
No incidence figures for specific side effects, broken down by symptom or by dose, are published in the material this page draws from, so none are stated here. Treat any specific side-effect percentage you see elsewhere attributed to SURMOUNT-5 with the same scrutiny this page applies to its own numbers, and check it against the source (DOI 10.1056/NEJMoa2416394).
Who tirzepatide is for, and who it isn’t
Tirzepatide has a specific, sourced reason behind it: it produced more weight loss than semaglutide in the only trial that has ever compared them directly, 20.2% versus 13.7% at 72 weeks. Anyone whose priority is the larger measured result, and who has been evaluated by a licensed prescriber as a candidate for a dual-agonist medication, has grounds to ask about tirzepatide specifically rather than semaglutide. See the full breakdown, including where semaglutide’s longer track record fits into that decision, on our semaglutide vs tirzepatide comparison.
Tirzepatide is not automatically the right starting point for everyone. SURMOUNT-5 enrolled adults with obesity who did not have type 2 diabetes, so its 20.2% figure describes that population specifically, not people with diabetes taking tirzepatide as Mounjaro, and it is a trial average across 751 people, not a promise for any one individual. Whether tirzepatide is appropriate for a given person, weighed against their health history and any other medications, is a decision for a licensed prescriber, not something a page like this one can settle in the abstract.
How to actually get it
Tirzepatide is FDA-approved and available today from a licensed prescriber after a medical evaluation. The providers below evaluate eligibility and prescribe compounded tirzepatide, the same active ingredient sold under the brand names Mounjaro and Zepbound. A compounded preparation carries the same active ingredient but is not itself an FDA-approved finished product, even when the compounding pharmacy is properly registered, which is worth knowing before you start.
These providers prescribe tirzepatide and semaglutide, which are FDA-approved. We may earn a commission, and it never changes your price.
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#1
TrimRxPersonalized programs, US pharmacies
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#2
Joi & BlokesHis & hers compounded GLP-1s
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#3
ReadyRxFast approvals on weight-loss meds
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The table below scores all five providers this site reviews against the same published rubric, including what each charges for tirzepatide as the prescribed dose rises. Read our full TrimRx review for the most detailed look at one of them.
| # | Provider | Our score | Semaglutide | Tirzepatide | Worth knowing |
|---|---|---|---|---|---|
| 1 | TrimRx | 3.0/5 | from $199/mo | from $349/mo | Price stays flat as the dose escalates. |
| 2 | Joi & Blokes | 2.0/5 | $199/mo, billed quarterly | $299/mo, billed quarterly | First payment is $497 (semaglutide) or $747 (tirzepatide). |
| 3 | ReadyRx | 2.0/5 | $299/mo, or $249/mo prepaid | $399/mo | Refund if you have not lost 5% of baseline weight by 28 weeks. |
| 4 | AltRx | 0.5/5 | $89/mo promotional, $199/mo standard | $149/mo | BBB rates it F for failure to respond to 37 complaints. |
| 5 | Zevay | 0.0/5 | $149/mo | $187/mo | No BBB or Trustpilot profile found as of 16 July 2026. |
Scores are computed from our published rubric, shown in full on each review. Prices verified 16 July 2026: confirm your current price with the provider before you pay.
Sources
Aronne LJ, Horn DB, le Roux CW, Ho W, et al. “Tirzepatide as Compared with Semaglutide for the Treatment of Obesity.” New England Journal of Medicine, 3 July 2025. DOI: 10.1056/NEJMoa2416394. PMID 40353578. Registered as ClinicalTrials.gov NCT05822830. This is the primary source for every SURMOUNT-5 figure on this page.
How tirzepatide works: frequently asked questions
How does tirzepatide cause weight loss?
Tirzepatide activates two hormone receptors, GLP-1 and GIP, which together slow stomach emptying, reduce appetite signaling in the brain, and affect insulin response. That dual-receptor activation is the mechanistic explanation for why tirzepatide produced more weight loss than semaglutide, which activates GLP-1 alone, in the SURMOUNT-5 trial (Aronne LJ, Horn DB, le Roux CW, Ho W, et al., NEJM, 2025).
What is the difference between tirzepatide and semaglutide?
Tirzepatide is a dual GIP and GLP-1 receptor agonist; semaglutide is a GLP-1 receptor agonist alone. In the only randomised trial that compared them directly, tirzepatide produced more weight loss, 20.2% versus 13.7% at 72 weeks. See the full comparison, including the trial’s limits, on our semaglutide vs tirzepatide page.
Is tirzepatide FDA-approved for weight loss?
Yes. Tirzepatide is FDA-approved for weight loss under the brand name Zepbound, and separately FDA-approved for type 2 diabetes under the brand name Mounjaro. Both brand names contain the same active ingredient.
What is the difference between Mounjaro and Zepbound?
Nothing in the active ingredient. Both are tirzepatide. Mounjaro is the FDA-approved brand name for type 2 diabetes; Zepbound is the FDA-approved brand name for weight loss. The drug itself does not change between the two.
How often is tirzepatide injected?
Once weekly, by subcutaneous injection. That is the dosing schedule SURMOUNT-5 used for both its tirzepatide arm (maximum tolerated 10 or 15 mg) and its semaglutide arm (Aronne LJ, Horn DB, le Roux CW, Ho W, et al., NEJM, 2025).
Does tirzepatide cause more side effects than semaglutide?
SURMOUNT-5 reports gastrointestinal side effects as the most common in both the tirzepatide and semaglutide groups, mostly mild to moderate and occurring primarily during dose escalation, without publishing incidence figures broken out clearly enough in the available material to declare a clean winner between the two.
What about compounded tirzepatide?
Compounded tirzepatide contains the same active ingredient as Mounjaro and Zepbound, but a compounded preparation is not itself an FDA-approved finished product, even when the compounding pharmacy is properly registered. SURMOUNT-5 tested the drug itself, not a compounded version, so its results describe the active ingredient rather than any specific compounded formulation.
Is tirzepatide better than retatrutide?
No published trial has compared them directly, so there is no evidence-based answer to “better.” Retatrutide produced a larger number, −24.2% at 12 mg, in its own separate phase 2 trial (Jastreboff AM, Kaplan LM, Frías JP, et al., NEJM, 2023), but that trial differs from SURMOUNT-5 in design, duration and population, and retatrutide remains investigational: it cannot legally be prescribed today.