Foundayo Safety Explained: Side Effects, Warning Signs and Who Needs Extra Care

• Side effects and how often they happen, taken from the official UK leaflet and trial data
• Serious warning signs to act on, and the conditions that need a prescriber's review first
• Clear explanation of where UK and US safety information differ
• Online consultation with UK-registered prescribers to check whether Foundayo is suitable for you

Foundayo (orforglipron) is a once-daily GLP-1 tablet licensed in the UK for weight management and type 2 diabetes. Like every GLP-1 medicine, its most common side effects affect the digestive system: nausea, diarrhoea, vomiting, constipation and indigestion. These are usually mild to moderate and tend to ease as your body adjusts. A smaller number of serious side effects, such as pancreatitis and dehydration-related kidney problems, are rare but important to recognise early.

This guide brings together the safety information in Foundayo's official UK patient leaflet with the figures reported from its clinical trials. It explains what side effects to expect, which symptoms need urgent attention, who should speak to a prescriber before starting, how UK and US safety information differ, and how Foundayo's safety compares with Wegovy.

Key things to know

• Digestive side effects are the most common, affecting more than 1 in 10 people, and are most likely when starting or increasing the dose
• In the main weight management trials, most digestive side effects were mild (60%) or moderate (36%); 4% were severe
• Seek urgent medical help for severe stomach pain that spreads to your back and does not go away, as this can be a sign of pancreatitis
• Drinking enough fluids matters, because vomiting and diarrhoea can cause dehydration and, rarely, kidney problems
• Low blood sugar is mainly a risk when Foundayo is taken with insulin or a sulfonylurea
• Foundayo may make the contraceptive pill less effective for 30 days after starting and after each dose increase

Where Foundayo's UK Safety Information Comes From

In the UK, the official safety information is set out in two documents approved by the MHRA: the Summary of Product Characteristics (SmPC) for healthcare professionals, and the Patient Information Leaflet (PIL) in every pack. This guide follows the UK leaflet, revised in August 2026.

The US FDA authorised Foundayo in 2026, before the UK's 10 August 2026 authorisation. The US label includes some useful trial figures, which are quoted below where helpful. But it also contains US-specific wording, such as a boxed warning and an extra contraindication, that does not appear in the UK leaflet. Where the two differ, this guide says so.

The Most Common Side Effects

Side effects listed in the UK leaflet

The most common adverse events include nausea, vomiting and diarrhea.

How often digestive side effects happened in the trials

In the pooled placebo-controlled weight-management trials, gastrointestinal side effects occurred in 60.1% of people receiving the 6 mg hard-capsule dose, 67.4% receiving 12 mg and 68.7% receiving 36 mg, compared with 36.3% with placebo. The most commonly reported individual reactions included nausea, diarrhoea, constipation, vomiting and abdominal pain. Of the gastrointestinal reactions reported in these studies, 61.8% were mild, 34.3% were moderate and 3.9% were severe.

Why side effects are worst at the start

GLP-1 medicines slow the rate at which your stomach empties, and Foundayo may also affect the absorption of other oral medications, while acting on appetite signals in the brain. Both effects can cause nausea and fullness while your body adjusts. The trials found digestive side effects were highest during the dose-increase period and fell over time. This is why Foundayo starts at 0.8 mg for 30 days and increases step by step, with at least 30 days at each dose before moving up. Side effects can briefly return after each increase.

Practical ways to reduce digestive side effects

The UK product information advises taking precautions to avoid dehydration if vomiting or diarrhoea occurs. If gastrointestinal side effects are troublesome or severe, speak to your prescriber. Dose modification or discontinuation may need to be considered if severe gastrointestinal symptoms develop. Do not change your dose without medical advice.

Serious Side Effects: When to Get Help

Serious reactions are uncommon, but knowing the warning signs means you can act quickly. Some serious side effects can be life-threatening and need urgent medical assessment.

The US prescribing information reports acute kidney injury in 0.2% of people treated with Foundayo compared with 0.05% with placebo in clinical trials. Kidney problems can occur when vomiting or diarrhoea causes dehydration and volume depletion. The UK SmPC advises patients to take precautions to avoid dehydration.

Who Should Talk to a Prescriber Before Starting

The UK leaflet asks you to talk to your doctor, nurse or pharmacist before taking Foundayo in the following situations.

A history of pancreatitis

Foundayo has not been studied in people with a history of pancreatitis and should be used with caution. Acute pancreatitis is listed as an uncommon side effect, affecting up to 1 in 100 people.

Taking insulin or a sulfonylurea for type 2 diabetes

Foundayo can increase the risk of hypoglycaemia when used with insulin or a sulfonylurea such as gliclazide. In clinical studies, clinically significant hypoglycaemia occurred in 2% of Foundayo-treated patients compared with 0.2% with placebo in a relevant type 2 diabetes population. Among patients taking a sulfonylurea in that study, hypoglycaemia occurred in 6.7%. Your prescriber may consider reducing the dose of insulin or the sulfonylurea and may advise blood-glucose monitoring.

Severe digestive problems

Foundayo has not been studied in people with severe gastrointestinal disease, including severe gastroparesis, and should be used with caution in these patients. Tell your prescriber if you have a severe digestive condition.

Kidney problems

Dehydration from vomiting or diarrhoea is a particular concern if your kidneys already work less well.

Blood pressure medicines

Foundayo can lower blood pressure. If you take medicines for high blood pressure, your prescriber may need to adjust them.

Gallbladder problems

Gallstones are listed as a common side effect of Foundayo. Acute gallbladder events have been associated with weight reduction. Tell your prescriber if you have a history of gallbladder problems.

Diabetic eye disease

If you have diabetic retinopathy or macular oedema, tell your prescriber. Rapid improvements in blood sugar can temporarily affect diabetic eye disease.

Planned surgery or sedation

Because Foundayo slows stomach emptying, food or liquid may be more likely to enter the lungs during a general anaesthetic or deep sedation. Tell your surgical team and anaesthetist that you take Foundayo well before any procedure.

Severe heart failure

Tell your prescriber if you have or have had severe heart failure.

Who Cannot Take Foundayo: UK and US Differences

In the UK, the Foundayo SmPC lists hypersensitivity to orforglipron or any of its ingredients as the formal contraindication. The UK patient leaflet also says Foundayo should not be used during pregnancy or breastfeeding, and its safety and effectiveness have not been established in people under 18.

The US prescribing information has additional restrictions. It contraindicates Foundayo in people with a personal or family history of medullary thyroid carcinoma (MTC) or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), and carries a boxed warning concerning thyroid C-cell tumours. The FDA label states that orforglipron itself is not pharmacologically active in rats or mice and did not produce tumours in rodents; the relevance of GLP-1 receptor-dependent thyroid C-cell tumours seen with other GLP-1 receptor agonists in rodents to humans has not been determined.

These US-specific thyroid warnings and contraindications do not appear in the current UK Foundayo product information.

Pregnancy, Breastfeeding and Contraception

Foundayo should not be used during pregnancy, as its effects on an unborn baby are not known. The UK leaflet recommends using contraception while taking it and stopping at least 3 weeks before trying for a baby. It should not be used while breastfeeding.

One point is easy to miss. Foundayo may reduce how well oral hormonal contraceptives work. If you use the pill, the leaflet advises also using a barrier method such as condoms, or switching to a non-oral method, for 30 days after starting Foundayo and for 30 days after each dose increase.

Medicines That Interact With Foundayo

Foundayo can interact with medicines that affect its metabolism or transport, including some CYP3A4 inhibitors and inducers. Examples include clarithromycin, itraconazole, ketoconazole, ritonavir, carbamazepine, rifampicin, phenytoin and St John's wort. Foundayo can also affect exposure to some other medicines, including rosuvastatin, simvastatin and oral topotecan. It also delays gastric emptying, which can affect the absorption of some oral medicines. Always tell your prescriber about all medicines, supplements and herbal products you take.

Driving and Using Machines

There is no evidence from specific driving studies that Foundayo directly affects the ability to drive. However, if it is taken with insulin or a sulfonylurea, precautions are needed because hypoglycaemia can impair driving.

How Many People Stopped Because of Side Effects?

In ATTAIN-1, 5.3%, 7.9% and 10.3% of people stopped treatment because of side effects across the three doses, from lowest to highest, compared with 2.7% on placebo. In other words, around 9 in 10 people on the highest dose were able to continue. Stopping rates were also higher with Foundayo than with the comparison medicines in the diabetes head-to-head trials.

What About Liver Safety?

No hepatic safety signal was identified across the phase 3 clinical programme, and liver injury is not listed as an adverse reaction in the current UK Foundayo product information. Because Foundayo is newly authorised, longer-term safety information will continue to accumulate through clinical use and post-marketing monitoring.

How Does Foundayo's Safety Compare With Wegovy?

Wegovy (semaglutide) is available in the UK as a weekly injection and, since June 2026, as a once-daily tablet. Foundayo (orforglipron) is also a once-daily oral GLP-1 receptor agonist authorised for weight management. Both medicines commonly cause gastrointestinal side effects, but their clinical trial programmes and dosing regimens are different.

The main differences are in how they are taken and how much real-world experience exists.

There is currently no direct head-to-head trial establishing whether Foundayo has a different overall safety profile from Wegovy. Both medicines commonly cause gastrointestinal side effects, but results from separate clinical trials should not be treated as a direct comparison because the study populations, designs and treatment regimens differ. Foundayo is newly authorised, so its post-marketing safety experience is more limited.

Additional Monitoring and Reporting Side Effects

Foundayo carries a black triangle, meaning it is under additional monitoring as a newly authorised medicine. This is standard for new medicines and does not mean a specific problem has been found. It means regulators want new safety information identified quickly.

You can help by reporting any suspected side effect through the MHRA Yellow Card scheme, online or through the Yellow Card app, even if you are not sure the medicine caused it. Every report adds to the picture of how Foundayo performs outside clinical trials.

Getting a Safety Check Before You Start

Safety information describes risks across groups of people. Whether Foundayo is appropriate for an individual depends on their medical history, other medicines, contraception and treatment goals. A suitably qualified UK prescriber should assess these factors before prescribing.