Foundayo side effects: what the label and the ATTAIN trials show, and what's still unknown

What are the most common Foundayo side effects?

Foundayo (orforglipron) is a once-daily pill from Eli Lilly, approved by the FDA on 1 April 2026 for weight reduction and long-term maintenance in adults with obesity, or overweight plus a weight-related condition. Unlike semaglutide, it is a small, non-peptide molecule, and the label lets you take it with or without food.

Its prescribing information (revised July 2026) reports side effects from two 72-week placebo-controlled trials: ATTAIN-1 (adults without diabetes) and ATTAIN-2 (adults with type 2 diabetes), with 3,155 people on the drug.

Side effect	Placebo	5.5 mg	9 mg	17.2 mg
Nausea	10%	26%	34%	35%
Diarrhea	11%	21%	23%	25%
Constipation	9%	20%	27%	24%
Vomiting	4%	13%	21%	24%
Indigestion	4%	12%	16%	13%
Belly pain	7%	13%	14%	14%
Headache	7%	8%	9%	9%
Bloating	3%	7%	9%	8%
Fatigue	4%	6%	7%	9%
Burping	1%	6%	8%	8%
Acid reflux (GERD)	2%	6%	6%	7%
Gas	2%	5%	6%	6%
Hair loss	2%	4%	4%	5%

Foundayo US label, Table 1. The trials used an investigational formulation; the label shows results at the equivalent tablet doses. The published papers call the same arms 6, 12 and 36 mg.

A few Foundayo-specific patterns:

• Vomiting climbed steeply with dose, from 13% at 5.5 mg to 24% at 17.2 mg.
• Headache is on the common list, though only slightly above placebo (8–9% vs 7%).
• Heart rate rose by 4–5 beats per minute on average (0.5 on placebo), and a fast heart rate (tachycardia) was reported in 3% vs 0.9%.
• Hair loss was mainly reported by women (7% vs 0.9% of men) and was linked to weight reduction.

When do Foundayo side effects start, and do they ease?

The dose climbs slowly to limit stomach effects. You start at 0.8 mg daily for at least 30 days, then 2.5 mg for at least 30 days, then 5.5 mg. After that, your prescriber may step up to 9, 14.5 and 17.2 mg, each after at least 30 days, based on response and tolerability.

The label says nausea, vomiting and diarrhea were more frequent during dose escalation and decreased over time; the ATTAIN-2 authors describe the same pattern. Across both trials, 8% stopped Foundayo because of side effects (6% at 5.5 mg, 10% at 17.2 mg) vs 3% on placebo, mostly because of stomach symptoms.

One rule is unique to a daily pill: if you miss 7 or more doses in a row, the label says to restart at a lower dose to avoid a fresh wave of GI effects. Don’t double up after a missed day, and call your prescriber before restarting after a longer gap.

How much do we really know about Foundayo’s safety?

Less than for older GLP-1 medicines, and it’s worth being clear about the gaps:

• Real-world use is short. Foundayo has been on the US market since April 2026.
• The label’s numbers come from two trials of an investigational formulation, up to 72 weeks long.
• The postmarketing list is borrowed from the class. Pancreatitis, bowel obstruction, severe constipation, anaphylaxis, angioedema, aspiration under anesthesia and kidney failure are listed as reports with GLP-1 receptor agonists generally. Lilly’s medical information page describes the list the same way.
• The thyroid warning is a class warning. Orforglipron isn’t active at rat or mouse GLP-1 receptors and didn’t cause tumors in rodents. The label still carries the boxed warning, because the human relevance of GLP-1-related thyroid tumors in rodents is unknown.

What are the serious side effects of Foundayo?

The label lists these warnings:

• Thyroid C-cell tumors (boxed warning). Don’t take Foundayo with a personal or family history of medullary thyroid carcinoma or MEN 2. Report a neck lump, trouble swallowing, shortness of breath or lasting hoarseness.
• Pancreatitis. Confirmed in 6 people on Foundayo (0.14 per 100 patient-years) vs 1 on placebo (0.04).
• Severe stomach problems. About 3% vs 1% on placebo. Foundayo isn’t recommended with severe gastroparesis.
• Kidney injury from dehydration. 0.2% vs 0.05%, mostly after vomiting, diarrhea or nausea caused fluid loss.
• Low blood sugar. In ATTAIN-2 (type 2 diabetes), 2% had glucose below 54 mg/dL vs 0.2% on placebo; it was 7% in people also taking a sulfonylurea.
• Allergic reactions. 0.5% vs 0.3%, including anaphylactic reactions.
• Gallbladder disease. Gallstones 1% vs 0.7%; gallbladder inflammation 0.4% vs 0.3%.
• Diabetic eye disease. Not studied in people needing urgent treatment for retinopathy or macular edema.
• Anesthesia. Foundayo slows stomach emptying; tell every care team before a procedure.
• Low blood pressure. 2% vs 0.5%, and 4% in people on blood pressure medicines.

Foundayo also has its own drug interactions. Strong CYP3A4 inhibitors raise its levels and cap the dose at 9 mg; strong CYP3A4 inducers, and strong inhibitors that also block OATP1B such as ritonavir, should be avoided; and simvastatin is limited to 20 mg a day. Share your full medicine list with your prescriber and pharmacist. Birth control pills may work less well: the label suggests a non-oral method, or adding a barrier method, for 30 days after starting and after each dose increase (see GLP-1s and birth control). Stop Foundayo if you become pregnant, and it isn’t recommended with severe liver impairment.

What helps with Foundayo side effects?

The basics are the same as for other GLP-1 medicines, and we cover each in depth:

• Nausea: small, slow, lower-fat meals and sips of fluid between them. See what helps GLP-1 nausea.
• Constipation: 27% at 9 mg, so add fiber gradually, drink enough and keep moving. See GLP-1 constipation relief.
• Low appetite: protein-first small meals, as in what to eat on a GLP-1.
• Hair shedding: see GLP-1 hair loss.
• Alcohol: it overlaps with nausea and dehydration; see alcohol and GLP-1s.

Because Foundayo can be taken with or without food, there’s no fasting window to plan around; pick a daily time you’ll remember. Don’t skip, double or change doses on your own to manage side effects.

When should you call a doctor about Foundayo side effects?

Get urgent care for:

• Severe belly pain that won’t go away, with or without vomiting, sometimes spreading to the back
• Swelling of the face, lips, tongue or throat, trouble breathing or swallowing, or a very fast heartbeat with dizziness
• Vomiting or diarrhea that stops you keeping fluids down

Call your doctor promptly for upper-belly pain with fever, yellow skin or eyes or clay-colored stools; low blood sugar symptoms if you take insulin or a sulfonylurea; vision changes with type 2 diabetes; a neck lump or lasting hoarseness; or any side effect that is severe or won’t settle.

What should you log on Foundayo?

• Each daily dose and the time you took it, plus any missed days (the 7-day rule matters)
• Your current step and the date you moved up
• Side effects with severity, and how many days after a step they peaked
• New medicines, because of the CYP3A4 and simvastatin interactions
• Weight trend, and glucose readings if you have diabetes

GLPMate’s Foundayo tracker logs daily doses with reminders, and the side-effect tracker records severity so you can bring a doctor report to your next visit. This article is educational only and not medical advice; talk to your doctor about any side effect that concerns you.

FAQ

FAQ

What are the most common side effects of Foundayo?

In the pooled ATTAIN-1 and ATTAIN-2 trials, the most common were nausea (26–35% vs 10% on placebo), diarrhea (21–25% vs 11%), constipation (20–27% vs 9%) and vomiting (13–24% vs 4%). Indigestion, belly pain, headache, bloating, fatigue, burping, reflux, gas and hair loss were also more common than on placebo.

How long do Foundayo side effects last?

The label says nausea, vomiting and diarrhea were more frequent during dose escalation and decreased over time. Doses step up no sooner than every 30 days, so expect the first days after each step to be the hardest. If side effects make a step hard to tolerate, talk to your prescriber rather than changing the dose yourself.

Is Foundayo safer than GLP-1 injections?

There's no head-to-head trial to answer that, and rates from different trials can't be compared directly. Foundayo carries the same types of warnings as other GLP-1 medicines, including the boxed thyroid warning, pancreatitis, gallbladder disease and kidney injury from dehydration. It was approved in April 2026, so long-term, real-world safety data are still limited.

What happens if I miss Foundayo for a week?

Take a missed dose as soon as you remember, but never take two tablets in one day. If you miss 7 or more days in a row, the label says to restart at a lower dose to reduce stomach side effects, so call your prescriber before restarting.