Foundayo vs Zepbound: Weight Loss, Side Effects, Switching and Cost
The short answer
No trial has compared them directly. In their own 72-week trials, Zepbound 15 mg took off 20.9% of body weight and Foundayo 17.2 mg took off 11.1%. Foundayo is a daily pill with no food rules and costs $149 to $349 a month self-pay; Zepbound is a weekly injection at $299 to $699. After stopping tirzepatide, switching to orforglipron kept about three quarters of the weight loss for a year.
Foundayo (orforglipron) and Zepbound (tirzepatide) are both Eli Lilly weight-loss medicines, but one is a daily pill and the other a weekly injection, and they have never been tested against each other. Every number below comes from each drug's own US label or trial, so the comparison is across trials, which the labels themselves warn against: "adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug" (Zepbound label).
Foundayo vs Zepbound side by side
| Foundayo | Zepbound | |
|---|---|---|
| What it is | Orforglipron, a small-molecule GLP-1 pill | Tirzepatide, a GIP and GLP-1 peptide injection |
| How taken | One tablet a day, any time, with or without food | One injection a week, any time of day |
| Doses | 0.8 mg to 17.2 mg, a step every 30 days or more | 2.5 mg to 15 mg, a step every 4 weeks or more |
| Weight trial | Trial 1 (ATTAIN-1), 72 weeks, no diabetes | SURMOUNT-1, 72 weeks, no diabetes |
| Mean weight change, top dose | -11.1% (17.2 mg) | -20.9% (15 mg) |
| Placebo in the same trial | -2.1% | -3.1% |
| Lost at least 20%, top dose | 18.4% | 56.7% |
| Nausea, top dose vs placebo | 35% vs 10% | 28% vs 8% |
| Stopped for side effects, top dose | 10% | 6.2% |
| Self-pay per month | $149 to $349 | $299 to $699 |
| Medicare GLP-1 Bridge ($50) | All strengths | KwikPen only |
Sources: Foundayo label and ATTAIN-1; Zepbound label and SURMOUNT-1; prices from LillyDirect Foundayo and LillyDirect Zepbound; Medicare from CMS.
Weight loss: Zepbound did about twice as much in its trial
Both pivotal trials ran 72 weeks in adults with obesity or overweight and no diabetes. The top dose of Zepbound took off 20.9% of body weight against 3.1% on placebo, a 17.8 point difference; the top dose of Foundayo took off 11.1% against 2.1%, a 9.0 point difference. In people with type 2 diabetes the gap was similar: 14.7% for Zepbound 15 mg, 9.6% for Foundayo 17.2 mg. Different trials enrol different people, so read these as orders of magnitude, not a ranking to the decimal. ClinicalTrials.gov lists no randomised orforglipron vs tirzepatide trial (registry search, 8 November 2026).
Switching from Zepbound to Foundayo
The one trial that links them is ATTAIN-MAINTAIN. People who had lost weight on tirzepatide 10 or 15 mg for 72 weeks switched straight to orforglipron (12 mg of the trial formulation, raised every 4 weeks) or to placebo. After a year, the orforglipron group had kept an estimated 74.7% of their weight loss, against 49.2% on placebo (ATTAIN-MAINTAIN, Nat Med 2026). They still regained about 5 points, and the trial had no arm that stayed on Zepbound, so it shows the pill holds much of the loss, not that it holds all of it. The Foundayo label gives no switching dose; Lilly tells patients to work out the transition with their doctor.
Side effects
Both labels are dominated by stomach and gut effects, worst while the dose goes up. Nausea at the top dose was 35% on Foundayo and 28% on Zepbound, vomiting 24% and 13%, constipation 24% and 11%. Zepbound adds injection-site reactions (8% at 15 mg). Both carry the boxed warning on thyroid C-cell tumours. With Foundayo, the label also asks women on oral contraceptives to add a barrier method for 30 days after starting and after each dose step.
Cost
Paying cash through LillyDirect, Foundayo runs $149 to $349 a month and Zepbound $299 to $699, with the lower top-dose price on each only if you refill within 45 days. Under Medicare's GLP-1 Bridge both cost a $50 copay, but only the Zepbound KwikPen qualifies, not the vials. Full breakdown: orforglipron price and tirzepatide cost.
Which one fits
On the trial data, Zepbound produces roughly twice the weight loss; Foundayo avoids needles and a fridge and costs less. That is a choice for a prescriber who knows your history. For the injection, see the Zepbound guide.
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Build your stack, 2 minutesFrequently asked questions
Is Foundayo as good as Zepbound?
For weight loss, not in the trials. Zepbound 15 mg took off 20.9% of body weight in 72 weeks against 11.1% for Foundayo 17.2 mg, in separate trials of similar people. No head-to-head trial exists.
Can you switch from Zepbound to Foundayo?
In ATTAIN-MAINTAIN, people who switched from tirzepatide to orforglipron kept an estimated 74.7% of their weight loss after a year, against 49.2% on placebo. The Foundayo label gives no switching dose, so the transition is set by the prescriber.
Is Foundayo tirzepatide in a pill?
No. Foundayo is orforglipron, a small-molecule drug that acts only on the GLP-1 receptor. Tirzepatide is a peptide that acts on both GIP and GLP-1 receptors and is only sold as an injection.
Which has fewer side effects, Foundayo or Zepbound?
Both mainly cause nausea, diarrhoea, vomiting and constipation. At the top doses nausea was 35% on Foundayo and 28% on Zepbound, and 10% vs 6.2% stopped for side effects, but these come from different trials and cannot be compared directly.
Is Foundayo cheaper than Zepbound?
Yes at self-pay prices: Foundayo $149 to $349 a month, Zepbound $299 to $699, as read on LillyDirect on 8 November 2026.
Sources (checked 8 November 2026)
- Foundayo (orforglipron) US prescribing information, revised 7/2026. Checked 8 November 2026.
- Zepbound (tirzepatide) US prescribing information, revised 08/2026. Checked 8 November 2026.
- Orforglipron, an oral small-molecule GLP-1 receptor agonist for obesity treatment (ATTAIN-1). N Engl J Med 2025;393(18):1796-1806. Checked 8 November 2026.
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med 2022. Checked 8 November 2026.
- Orforglipron for weight maintenance after tirzepatide or semaglutide (ATTAIN-MAINTAIN). Nat Med 2026;32(7):2679-2687. Checked 8 November 2026.
- ClinicalTrials.gov, studies with orforglipron as intervention, searched 8 November 2026. Checked 8 November 2026.
- LillyDirect, Foundayo self-pay pricing. Checked 8 November 2026.
- LillyDirect, Zepbound self-pay pricing. Checked 8 November 2026.
- CMS, Medicare GLP-1 Bridge information for pharmacies. Checked 8 November 2026.
Cross-trial comparison from each US label; prices as read on 8 November 2026. Labels and trial records change; the leaflet in your box and your prescriber come first. Educational content, not medical advice.