Drug facts
Foundayo (orforglipron) vs tirzepatide
Quick answer
Foundayo is not tirzepatide. It is orforglipron, a once-daily tablet that acts on one receptor, GLP-1. Tirzepatide, sold as Zepbound and Mounjaro, is a once-weekly injection that acts on two, GIP and GLP-1. Both are Eli Lilly products. No trial has compared them head to head. Read side by side from each label’s own 72-week trial in adults without diabetes, the top doses changed weight by −11.1% (Foundayo 17.2 mg) and −20.9% (tirzepatide 15 mg), against placebo changes of −2.1% and −3.1%. That is a cross-trial comparison, not a measured difference.
Is Foundayo tirzepatide?1
No. The FOUNDAYO label describes orforglipron as a GLP-1 receptor agonist that binds to and activates the human GLP-1 receptor. Its description section gives orforglipron calcium a molecular weight of 902.0 g/mol, and it is taken by mouth once a day. The ATTAIN-MAINTAIN trial report calls it a nonpeptide GLP-1 receptor agonist.7
The Zepbound label describes tirzepatide as a GIP receptor and GLP-1 receptor agonist, a peptide with a molecular weight of 4813.53 Da that carries a fatty diacid for albumin binding, injected under the skin once a week.2 They share one target and a manufacturer; they are not versions of each other.3 Every approved tirzepatide product, under both brand names, is recorded in Drugs@FDA as a solution for subcutaneous injection; Foundayo is recorded as an oral tablet. What is sold online as “oral tirzepatide” is covered in oral tirzepatide.
The two side by side2
| From each label | Foundayo (orforglipron) | Zepbound (tirzepatide) |
|---|---|---|
| Receptors | GLP-1 | GIP and GLP-1 |
| Form | Tablet, by mouth | Injection, under the skin |
| How often | Once daily, with or without food | Once weekly, any time of day |
| Starting dose | 0.8 mg | 2.5 mg |
| Dose steps | After at least 30 days on each dose | After at least 4 weeks on each dose |
| Maximum dose | 17.2 mg daily | 15 mg weekly |
| Half-life | About 29 to 49 hours | About 5 to 6 days |
| Steady state | About 1 week | After 4 weeks |
| Broken down by | Mainly the liver enzyme CYP3A4 | Proteolytic cleavage, beta-oxidation and amide hydrolysis |
| Storage | Room temperature, 20°C to 25°C (68°F to 77°F) | Refrigerated, 2°C to 8°C (36°F to 46°F) |
| Oral contraceptives | Switch or add a barrier method for 30 days after starting and after each increase | Switch or add a barrier method for 4 weeks after starting and after each increase |
| Boxed warning | Thyroid C-cell tumors | Thyroid C-cell tumors |
Two rows have practical weight. Because orforglipron is broken down by CYP3A4, its label caps the dose at 9 mg with a strong CYP3A4 inhibitor and limits simvastatin to 20 mg a day; the Zepbound label reports a low potential for tirzepatide to inhibit or induce CYP enzymes. And the contraception row is the same instruction on two clocks, with the FOUNDAYO label also advising effective contraception throughout treatment.6 Missed doses differ too. For Zepbound: If a dose is missed, take it within 4 days (96 hours); after that, skip it and take the next dose on the regular day. For Foundayo, the label says to take a missed dose as soon as possible without doubling up the next one, and to restart escalation at a lower dosage after 7 or more consecutive missed doses. The tirzepatide missed-dose rule →
Weight loss, in two separate trials4
Each label’s efficacy section reports a 72-week, double-blind, placebo-controlled trial in adults with obesity, or overweight with a weight-related condition, and without diabetes. They are separate trials, so each result is shown against its own placebo arm.
| Arm | Weight change | Difference from placebo |
|---|---|---|
| 17.2 mg daily | −11.1% | −9 |
| 9 mg daily | −8.3% | −6.2 |
| 5.5 mg daily | −7.4% | −5.3 |
| Placebo | −2.1% | — |
| Arm | Weight change | Difference from placebo |
|---|---|---|
| 15 mg weekly | −20.9% | −17.8 |
| 10 mg weekly | −19.5% | −16.4 |
| 5 mg weekly | −15.0% | −11.9 |
| Placebo | −3.1% | — |
The gap between the columns is large, but it was not measured in one trial, and the trials differ in ways that move results.5 FOUNDAYO’s Trial 1 enrolled a population that was 28% Asian, against 11% in SURMOUNT-1; a quarter or less of each FOUNDAYO arm stopped the trial drug (22% to 24%, against 30% on placebo), against 14.3% to 16.4% in SURMOUNT-1’s tirzepatide arms (26.4% on placebo). Only a trial that randomizes people between the two could say how much of the gap is the drugs. How SURMOUNT-1 unfolded over time is on tirzepatide weight loss results, week by week.
Side effects, from each label4
Both labels open their adverse-reaction section with the same sentence: rates observed in one drug’s trials “cannot be directly compared to rates in the clinical trials of another drug.” With that said, here are the four most common gastrointestinal reactions as each label reports them.
| Reaction | Placebo | 5.5 mg | 9 mg | 17.2 mg |
|---|---|---|---|---|
| Nausea | 10% | 26% | 34% | 35% |
| Constipation | 9% | 20% | 27% | 24% |
| Diarrhea | 11% | 21% | 23% | 25% |
| Vomiting | 4% | 13% | 21% | 24% |
| Reaction | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 8% | 25% | 29% | 28% |
| Constipation | 5% | 17% | 14% | 11% |
| Diarrhea | 8% | 19% | 21% | 23% |
| Vomiting | 2% | 8% | 11% | 13% |
Stopping because of side effects: across Foundayo’s two trials, 6%, 9% and 10% at 5.5, 9 and 17.2 mg, against 3% on placebo. Across Zepbound’s two, 4.8%, 6.3% and 6.7% at 5, 10 and 15 mg, against 3.4% on placebo.5 Both pools include a trial in type 2 diabetes. The full tirzepatide table is on the side-effects page.
The one trial that involves both7
ATTAIN-MAINTAIN took people who had been treated with an injection in the SURMOUNT-5 trial and randomized them to orforglipron or placebo. In the 205 who had been on tirzepatide, those who reached a weight plateau kept an estimated 74.7% of their weight reduction at week 52 on orforglipron, against 49.2% on placebo.
That is a switching trial, not a comparison. The authors list the limitation themselves: there was no arm that stayed on the injection, so it cannot say whether switching kept as much as continuing would have. What happened to people who stopped tirzepatide outright is measured in SURMOUNT-4.
No head-to-head trial8
No trial has randomized people to orforglipron against tirzepatide. Of the 53 studies listing orforglipron as an intervention on ClinicalTrials.gov in September 2026, none compares the two; the nearest is ATTAIN-MAINTAIN, above. Until one does, any claim that one drug works a set amount better than the other is a cross-trial estimate, whoever makes it. The trial evidence that does exist for tirzepatide against another GLP-1 drug is on tirzepatide vs semaglutide.
Where compounded tirzepatide fits
On the label — Mounjaro / Zepbound
Every figure on this page comes from the approved products, Foundayo and Zepbound, as reported in their FDA prescribing information.
In a compounded vial
A compounded tirzepatide vial is neither of them, and no trial has compared it with Foundayo or with Zepbound. What is actually different →
This site’s price index covers compounded tirzepatide and states each seller’s price as a true calendar month. It does not price Foundayo.
Nothing here is medical advice, and this page does not recommend one drug over the other. Which medicine, if any, suits a person is a question for a prescriber who knows their history. See the medical disclaimer.
Questions
- Is Foundayo tirzepatide?
- No. Foundayo is orforglipron, a once-daily tablet that activates the GLP-1 receptor. Tirzepatide, sold as Zepbound and Mounjaro, is a once-weekly injection that activates both the GIP and GLP-1 receptors. Both are made by Eli Lilly.
- Is Foundayo as effective as Zepbound?
- No trial has compared them. In each label's own 72-week trial in adults without diabetes, weight changed by -11.1% on Foundayo 17.2 mg against -2.1% on placebo, and by -20.9% on Zepbound 15 mg against -3.1% on placebo. Those are separate trials, so the difference between them is a cross-trial comparison.
- What is the difference between orforglipron and tirzepatide?
- Orforglipron is a nonpeptide GLP-1 receptor agonist taken by mouth once a day, with a half-life of about 29 to 49 hours. Tirzepatide is a peptide that activates GIP and GLP-1 receptors, injected once a week, with a half-life of about 5 to 6 days.
- Can you switch from Zepbound to Foundayo?
- The ATTAIN-MAINTAIN trial switched people who had lost weight on tirzepatide to orforglipron or placebo; those who reached a plateau kept an estimated 74.7% of their weight reduction at week 52 on orforglipron, against 49.2% on placebo. It had no arm that stayed on tirzepatide. Whether to switch is a decision for a prescriber.
- Is there a tirzepatide pill?
- No FDA-approved tirzepatide is taken by mouth; every approved tirzepatide product is an injection. The approved weight-loss pill from the same company is Foundayo, which contains orforglipron.
Sources
- FDA prescribing information for FOUNDAYO (orforglipron) tablets, sections 1, 2, 11, 12 and 16, revision 7/2026
- FDA prescribing information for ZEPBOUND (tirzepatide), sections 1, 2, 11, 12 and 16, revision 8/2026 DailyMed
- Drugs@FDA via openFDA, applications with active ingredient TIRZEPATIDE (NDA 215866, NDA 217806) and ORFORGLIPRON (NDA 220934), Eli Lilly and Co, queried September 2026
- FDA prescribing information for FOUNDAYO (orforglipron) tablets, sections 6.1 and 14, revision 7/2026
- FDA prescribing information for ZEPBOUND (tirzepatide), sections 6.1 and 14.1, revision 8/2026 DailyMed
- FDA prescribing information for FOUNDAYO (orforglipron) tablets, sections 7.3, 8.1 and 8.3, revision 7/2026
- Aronne LJ, et al. Orforglipron for maintenance of body weight reduction: the double-blind, randomized phase 3b ATTAIN-MAINTAIN trial. Nature Medicine. 2026;32(7):2679-2687. PMID 42120723
- ClinicalTrials.gov, studies listing orforglipron as an intervention (53 records), searched September 2026