The most common Foundayo side effects are digestive: feeling sick (nausea), constipation, diarrhoea, being sick, indigestion and stomach pain. The UK patient leaflet lists each as very common (may affect more than 1 in 10 people). They are usually not severe, are most likely when you start or step up a dose, and tend to ease over time. Less common but more serious risks include pancreatitis, gallbladder problems and kidney problems caused by dehydration.
Foundayo (orforglipron) was authorised by the MHRA on 10 August 2026; its UK Summary of Product Characteristics (SmPC) and patient leaflet are on the emc. This is information only, not medical advice: Foundayo is a prescription-only medicine, and a qualified prescriber decides whether it suits you.
What are the most common Foundayo side effects?
The leaflet's frequency groups:
- Very common (may affect more than 1 in 10): nausea, constipation, diarrhoea, vomiting, indigestion and stomach pain. Low blood sugar is also very common with insulin in type 2 diabetes.
- Common (up to 1 in 10): dizziness, headache, a fast pulse, low blood pressure, bloating, burping, reflux or heartburn, wind, gallstones, hair loss, tiredness and raised pancreatic enzymes in blood tests; also low blood sugar alongside a sulfonylurea.
- Uncommon (up to 1 in 100): acute pancreatitis, an unusual sense of taste, an unpleasant, abnormal feeling when touched, and low blood sugar without insulin or a sulfonylurea.
Our side effects page has the dose-by-dose ATTAIN-1 figures.
How often did stomach side effects happen in the trials?
The UK SmPC pools the two weight-management trials, ATTAIN-1 and ATTAIN-2 (4,740 adults). They used capsules; the SmPC names the tablet strength with an equal effect:
- 5.5 mg tablet (6 mg capsule): 60.1% had a gastrointestinal side effect
- 9 mg tablet (12 mg capsule): 67.4%
- 17.2 mg tablet (36 mg capsule): 68.7%
- Placebo: 36.3%
The medicine's own effect is the gap over placebo. Among people on orforglipron who had these effects, they were mild for 61.8%, moderate for 34.3% and severe for 3.9%.
Nausea was the most common single side effect: 26%, 34% and 35% at those three tablet doses versus 10% on placebo, according to the US prescribing information.
Do Foundayo side effects wear off?
For most people they ease. The SmPC says nausea, vomiting and diarrhoea were more frequent during dose escalation and then decreased, and in the ATTAIN-1 trial gut side effects began mainly during escalation. Orforglipron slows stomach emptying, an effect that is largest after the first dose; see how orforglipron works.
That is why the dose climbs slowly, at least 30 days per step: 0.8 mg, 2.5 mg, then 5.5 mg, with optional rises to 9, 14.5 and 17.2 mg depending on response and tolerability (see our dosage guide).
How many people stopped because of side effects?
In ATTAIN-1 (72 weeks, 3,127 adults without diabetes), 5.3% to 10.3% on orforglipron stopped because of any adverse event, versus 2.7% on placebo. In the SmPC's pooled data, 3.7%, 6.3% and 6.8% stopped because of gut side effects at those three tablet-equivalent doses, versus 0.6% on placebo.
Can Foundayo affect heart rate, blood pressure, hair or the gallbladder?
From the SmPC's pooled trials:
- Pulse: average pulse generally peaked during dose escalation at 6.7 to 8.6 beats per minute above baseline, falling to 3.9 to 5.2 above by week 72. A fast heart rate affected 2.7% versus 0.8% on placebo.
- Blood pressure: low blood pressure is common and happened more often in people taking blood pressure medicines, whose dose may need changing.
- Hair loss: 3.7% versus 1.8%, transient and associated with weight reduction.
- Gallstones: 1.3% versus 0.6%. Gallbladder symptoms in the leaflet include upper stomach pain, yellow skin or eyes, clay-coloured stools and fever.
Which Foundayo side effects are serious?
Pancreatitis is uncommon; the leaflet lists the others below as frequency not known, reported with this type of medicine.
- Acute pancreatitis: severe stomach and back pain that does not go away. The leaflet calls it potentially life-threatening and says to see a doctor immediately. ATTAIN-1 recorded five adjudication-confirmed cases, all mild and all in the orforglipron groups.
- Dehydration and kidney problems: vomiting and diarrhoea can dehydrate you, so the leaflet stresses drinking enough fluids; kidney problems, sometimes needing dialysis, have been reported.
- Bowel obstruction or severe constipation: severe tummy pain, a swollen tummy, vomiting, or being unable to pass wind or open your bowels.
- Serious allergic reaction: breathing problems, swelling of the face and throat, wheezing, or feeling dizzy or weak. Get immediate medical help.
- Sudden vision changes: tell your doctor.
- Surgery or sedation: the chance of food or liquid getting into the lungs may increase, so tell the team you take Foundayo.
Does Foundayo carry a thyroid cancer warning in the UK?
Not as a formal warning. The US prescribing information (revised July 2026) has a boxed warning about thyroid C-cell tumours in rodents given GLP-1 medicines active in those animals, and rules Foundayo out for anyone with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2. The UK SmPC has no thyroid warning, and its only contraindication is allergy to orforglipron or its ingredients. Its preclinical section says orforglipron is not pharmacologically active in rodents and did not cause cancer in rodent studies; the human relevance of thyroid findings with other GLP-1 medicines is considered low but cannot be completely excluded. ATTAIN-1 reported no medullary thyroid cancers. Tell your prescriber your full medical and family history.
Does Foundayo affect contraception, pregnancy or other medicines?
Foundayo may make the contraceptive pill less effective, so the SmPC advises a non-oral method or an added barrier method for 30 days after starting and after each dose increase. It should not be used in pregnancy or breastfeeding, and should be stopped at least 3 weeks before a planned pregnancy. Some antibiotics, antifungals, antivirals, epilepsy medicines and St John's wort can change orforglipron levels, so tell your prescriber and pharmacist everything you take.
How do I report a Foundayo side effect in the UK?
Foundayo carries the black triangle: it is under additional monitoring so new safety information can be identified quickly. Tell your doctor, nurse or pharmacist about suspected side effects, and report them to the MHRA Yellow Card scheme, online or via its app.
As of September 2026, Foundayo is not available on the NHS. NICE is appraising it for overweight and obesity (ID6516), with guidance provisionally expected on 27 January 2027; our UK availability page tracks this. Avoid any website offering Foundayo or a "compounded" version without a prescription: there is no way to know what such products contain.
Frequently asked questions
What is the most common side effect of Foundayo?
Nausea. It is one of six digestive effects the UK leaflet lists as very common (may affect more than 1 in 10 people), and in the two main weight-management trials it affected 26% to 35% of people across the 5.5, 9 and 17.2 mg doses, against 10% on placebo (US prescribing information).
How long do Foundayo side effects last?
There is no fixed timescale. The UK SmPC and leaflet say nausea, vomiting and diarrhoea are most common while starting or increasing the dose and decrease over time in most patients. Discuss severe or persistent side effects with your prescriber.
Can Foundayo cause hair loss?
Yes, it is listed as common. In the pooled weight-management trials it affected 3.7% on orforglipron and 1.8% on placebo, and the SmPC calls it transient and associated with weight reduction.
Does Foundayo stop the contraceptive pill working?
It may make oral hormonal contraceptives less effective. The UK SmPC advises switching to a non-oral method, or adding a barrier method, for 30 days after starting and for 30 days after each dose increase.
When should I get urgent medical help?
The leaflet says to see a doctor immediately for severe, persistent stomach pain that may reach the back, and to get immediate help for serious allergic reaction signs such as breathing problems or a swollen face or throat. Severe tummy pain with swelling or vomiting, or dehydrating vomiting or diarrhoea, also needs prompt advice.
More answers are on our FAQ page.