Key facts
- The most common Foundayo side effects are nausea (26% to 35%), constipation (20% to 27%), diarrhoea (21% to 25%) and vomiting (13% to 24%), against 4% to 11% on placebo.[1]
- GI side effects were mostly mild or moderate (60% mild, 36% moderate, 4% severe) and were most frequent while the dose was being raised, then decreased over time.[1]
- 8% of people on Foundayo stopped treatment because of adverse reactions in the pooled weight trials, against 3% on placebo.[1]
- The label carries a boxed warning on thyroid C-cell tumours, and Foundayo is contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2.[1]
- Women using oral contraceptives are advised to switch method or add a barrier method for 30 days after starting and after each dose increase.[1]
Most Common Foundayo Side Effects
Nausea is the most common Foundayo side effect, reported by 26% on 5.5 mg, 34% on 9 mg and 35% on 17.2 mg against 10% on placebo, in a pool of two 72-week trials of 3,155 people treated with Foundayo.[1]
| Adverse reaction | Placebo (n = 1,576) | 5.5 mg (n = 1,051) | 9 mg (n = 1,055) | 17.2 mg (n = 1,049) |
|---|---|---|---|---|
| Nausea | 10% | 26% | 34% | 35% |
| Constipation | 9% | 20% | 27% | 24% |
| Diarrhoea | 11% | 21% | 23% | 25% |
| Vomiting | 4% | 13% | 21% | 24% |
| Indigestion (dyspepsia) | 4% | 12% | 16% | 13% |
| Abdominal pain | 7% | 13% | 14% | 14% |
| Headache | 7% | 8% | 9% | 9% |
| Bloating (abdominal distension) | 3% | 7% | 9% | 8% |
| Fatigue | 4% | 6% | 7% | 9% |
| Belching (eructation) | 1% | 6% | 8% | 8% |
| Acid reflux (GORD) | 2% | 6% | 6% | 7% |
| Flatulence | 2% | 5% | 6% | 6% |
| Hair loss | 2% | 4% | 4% | 5%[1] |
FDA label, Table 1 (Trials 1 and 2, up to 72 weeks).
Taken together, GI adverse reactions affected 60% on 5.5 mg, 68% on 9 mg and 69% on 17.2 mg, against 37% on placebo.[1] The trials used an investigational orforglipron formulation, and the label shows the results as equivalent doses of the marketed tablet.[1] Figures here come from the label revised 07/2026, the labelling supplement the FDA approved on 4 August 2026.[2] For what orforglipron is and how well it works, see what is orforglipron.
Foundayo is not sold in this shop, and this page is not a guide to obtaining it. It summarises the FDA label and published trial data for reference.
Boxed Warning: Thyroid C-Cell Tumours
Yes, Foundayo has a boxed warning on thyroid C-cell tumours, although orforglipron is not pharmacologically active in rats or mice and did not produce tumours in rodents; the warning reflects GLP-1 class findings whose human relevance is not determined.[1]
- Contraindication. Foundayo must not be used by people with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).[1]
- Symptoms to report. The label lists a mass in the neck, difficulty swallowing, shortness of breath and persistent hoarseness as possible thyroid tumour symptoms.[1]
- Class evidence. Cases of MTC have been reported after marketing with liraglutide, another GLP-1 receptor agonist, but the data cannot establish or exclude a causal link.[1]
- Screening. Routine calcitonin tests or thyroid ultrasound are described as of uncertain value for early detection of MTC; people with MTC usually have calcitonin above 50 ng/L.[1]
Serious Warnings and Precautions
The label lists nine warnings and precautions; in the pooled trials, confirmed acute pancreatitis occurred in 6 people on Foundayo (0.14 per 100 patient-years) against 1 on placebo (0.04).[1]
| Warning (label section) | What the label says | Trial figure, Foundayo vs placebo |
|---|---|---|
| Thyroid C-cell tumours (5.1) | Boxed warning; contraindicated with MTC or MEN 2 | Not active in rodents; no rodent tumours[1] |
| Acute pancreatitis (5.2) | Stop if pancreatitis is suspected; watch for severe abdominal pain, sometimes radiating to the back | 0.14 vs 0.04 patients per 100 years of exposure[1] |
| Severe GI reactions (5.3) | Not recommended in severe gastroparesis | Severe GI reactions about 3% vs 1%[1] |
| Acute kidney injury from dehydration (5.4) | Monitor kidney function if vomiting, diarrhoea or nausea could cause fluid loss, especially when starting or raising the dose | 0.2% vs 0.05%[1] |
| Hypoglycaemia (5.5) | Risk rises with insulin or sulfonylureas; their dose may need lowering | Type 2 diabetes trial: 2% vs 0.2%; 7% with a sulfonylurea vs 0.5% without[1] |
| Hypersensitivity (5.6) | Anaphylaxis and angioedema reported with GLP-1 drugs; stop and seek care | 0.5% vs 0.3%[1] |
| Diabetic retinopathy in type 2 diabetes (5.7) | Rapid glucose improvement can temporarily worsen retinopathy; monitor those with a history | No rate given[1] |
| Acute gallbladder disease (5.8) | Linked with weight reduction; investigate if cholecystitis is suspected | Gallstones 1% vs 0.7%; cholecystitis 0.4% vs 0.3%[1] |
| Pulmonary aspiration under anaesthesia (5.9) | Tell the care team before surgery or deep sedation | Rare postmarketing reports with GLP-1 drugs[1] |
- The July 2026 label does not include a warning on suicidal behaviour or ideation; the word does not appear in the prescribing information.[1]
- Foundayo may cause fetal harm and should be stopped when pregnancy is recognised; it is not recommended while breastfeeding or in severe liver impairment (Child-Pugh C).[1]
- No dose change is recommended for kidney impairment, including end-stage renal disease.[1]
- Postmarketing reports with GLP-1 drugs include ileus, intestinal obstruction and severe constipation with faecal impaction.[1]
Other Side Effects on the Label
Beyond the common list, the label reports a heart rate rise of 4 to 5 beats per minute (placebo 0.5), tachycardia in 3% against 0.9%, and low blood pressure in 2% against 0.5%.[1]
- Low blood pressure. Hypotension was seen in 4% of people on Foundayo who also took blood pressure medicines, against 1% of those who did not.[1]
- Dizziness. 4% against 3% on placebo.[1]
- Taste change (dysgeusia). 0.9% against 0.3%.[1]
- Abnormal skin sensation (dysaesthesia). 0.3% on 9 mg and 1% on 17.2 mg, none on 5.5 mg, against 0.1% on placebo.[1]
- Pancreatic enzymes. Mean amylase rose 16% to 20% and lipase 26% to 31%, against 3% and 4% on placebo; the significance without pancreatitis symptoms is unknown.[1]
- QT interval. No clinically significant QTc prolongation at 1.4 times the peak levels of the 17.2 mg dose.[1]
When Do Foundayo Side Effects Start and How Long Do They Last?
Nausea, vomiting and diarrhoea were most frequent during the dose escalation period, when the dose rises in steps of at least 30 days from 0.8 mg, and decreased over time.[1]
- Escalation is the GI-risk window. The label sets the 0.8 mg start and 30-day steps (0.8, 2.5, 5.5, then 9, 14.5 or 17.2 mg) specifically to reduce GI side effects.[1]
- Stomach emptying slows most at first. The delay in gastric emptying is largest after the first dose and diminishes over time.[1]
- Restarting resets the risk. After 7 or more missed doses in a row, the label advises restarting escalation at a lower dose to reduce GI reactions.[1]
- The drug lingers for days. Half-life is about 29 to 49 hours and steady state takes about 1 week, so effects do not stop the day a dose is missed.[1]
The label does not give a typical duration in days or weeks for any individual side effect.[1]
How Many People Stop Foundayo Because of Side Effects?
8% of people on Foundayo permanently stopped because of adverse reactions in the pooled weight trials (5.5 mg 6%, 9 mg 9%, 17.2 mg 10%), against 3% on placebo, and most of them (5%) stopped for GI reactions.[1]
| Measure | Placebo | 5.5 mg | 9 mg | 17.2 mg |
|---|---|---|---|---|
| Stopped due to any adverse reaction | 3% | 6% | 9% | 10%[1] |
| Stopped due to GI adverse reactions | 0.7% | 3% | 6% | 6%[1] |
| Stopped trial drug for any reason, Trial 1 (no diabetes) | 30% | 22% | 22% | 24%[1] |
| Stopped trial drug for any reason, Trial 2 (type 2 diabetes) | 20% | 19% | 22% | 20%[1] |
Foundayo Drug Interactions
The label caps Foundayo at 9 mg a day with a strong CYP3A4 inhibitor, limits simvastatin to 20 mg a day, and advises a non-oral or added barrier contraceptive for 30 days after starting and after each dose increase.[1]
| Medicine or group | Label advice | Reason |
|---|---|---|
| Strong CYP3A4 inhibitors | Maximum Foundayo dose 9 mg once daily | Raise orforglipron exposure and side-effect risk[1] |
| Strong CYP3A4 inhibitors that also block OATP1B (e.g. ritonavir) | Avoid | Expected to raise levels significantly[1] |
| Strong CYP3A4 inducers | Avoid | Lower exposure, may reduce effect[1] |
| Moderate CYP3A4 inducers | Monitor effect, escalate dose as needed | Lower exposure[1] |
| Simvastatin | Do not exceed 20 mg once daily | Simvastatin acid exposure doubled[1] |
| Insulin or sulfonylureas | Consider lowering their dose when starting | Higher hypoglycaemia risk[1] |
| Oral hormonal contraceptives | Switch to non-oral, or add a barrier method, for 30 days after starting and after each dose increase | Slower stomach emptying may affect absorption; not tested in a clinical trial[1] |
| Another GLP-1 receptor agonist | Not recommended together | Limitation of use[1] |
Non-oral hormonal contraceptives, such as patches, rings, implants or injections, should not be affected, according to the label.[1]
Side Effects in the ATTAIN-1 Trial
In ATTAIN-1 (3,127 adults with obesity and no diabetes, 72 weeks), adverse events led to stopping treatment in 5.3% to 10.3% of people on orforglipron against 2.7% on placebo.[3]
- The most common adverse events were gastrointestinal and mostly mild to moderate.[3]
- The authors describe the adverse-event profile as consistent with other GLP-1 receptor agonists.[3]
- Trial doses were 6, 12 and 36 mg of the investigational formulation, which the label presents as 5.5, 9 and 17.2 mg tablets.[3][1]
- The PubMed abstract does not give per-event rates; the per-dose rates above come from the label’s pool of ATTAIN-1 and ATTAIN-2.[3][1]
Foundayo vs Eloralintide Side Effects
Both cause nausea, but the profiles differ: Foundayo’s top dose gave nausea in 35% against 10% on placebo, while in the eloralintide phase 2 trial nausea ranged from 11% to 64% by dose and fatigue reached 43% to 46%, against 12% on placebo.[1][4]
Foundayo is an approved GLP-1 pill; eloralintide is an investigational weekly amylin injection, and its fatigue signal stands out more than with Foundayo, where fatigue was 6% to 9% against 4% on placebo.[1][4] The trials differ in size, length and population, so the numbers are not directly comparable. For the amylin side, see eloralintide side effects, and for other approaches see GLP-1 alternatives.
Frequently Asked Questions
What are the most common side effects of Foundayo?
Nausea, constipation, diarrhoea, vomiting, indigestion, abdominal pain, headache, bloating, fatigue, belching, acid reflux, flatulence and hair loss, each in at least 5% of people in one or more dose groups. Nausea was the most common, at 26% to 35% depending on dose against 10% on placebo.
How long do Foundayo side effects last?
The label says nausea, vomiting and diarrhoea were most frequent during dose escalation and decreased over time, but it does not give a duration in days or weeks. Orforglipron has a half-life of about 29 to 49 hours, so effects can persist for a few days after a dose.
Does Foundayo cause nausea?
Yes. In the pooled 72-week weight trials, nausea affected 26% on 5.5 mg, 34% on 9 mg and 35% on 17.2 mg, against 10% on placebo. Most GI reactions were mild or moderate, and only 4% of those affected had severe reactions.
Does Foundayo cause hair loss?
Hair loss is on the label’s common list: 4% to 5% on Foundayo against 2% on placebo. The label links it to weight reduction and reports it more often in women (7%) than men (0.9%) on Foundayo.
Is Foundayo safe for the thyroid?
The label carries a boxed warning on thyroid C-cell tumours as a GLP-1 class warning. Orforglipron did not cause tumours in rodents, but it is not active in rats or mice, so the human relevance is not known. Foundayo is contraindicated in people with a personal or family history of medullary thyroid carcinoma or with MEN 2.
Does Foundayo affect birth control?
It may reduce the effect of oral contraceptive pills because it slows stomach emptying. The label advises switching to a non-oral method or adding a barrier method for 30 days after starting Foundayo and for 30 days after each dose increase.
Sources
- FDA. FOUNDAYO (orforglipron) tablets prescribing information, revised 07/2026 (NDA 220934, supplement 3)
- FDA. Drugs@FDA, NDA 220934 (Foundayo) approval history
- Wharton S, et al. Orforglipron, an oral small-molecule GLP-1 receptor agonist for obesity treatment (ATTAIN-1). N Engl J Med 2025;393(18):1796-1806. DOI 10.1056/NEJMoa2511774
- Billings LK, et al. Eloralintide phase 2, 48-week trial. The Lancet 2025;406:2631-2643. DOI 10.1016/S0140-6736(25)02155-5
For research use only. Not for human or veterinary consumption. This guide summarises published research for information only. It is not medical advice and does not describe any use of products sold on this site.