The main Foundayo drug interactions involve medicines that change how quickly your body clears orforglipron, the active ingredient. Some antibiotics, antifungals and antivirals push its level up, so the UK label caps the dose at 9 mg or rules them out; rifampicin, two epilepsy medicines and St John's wort pull it down and should be avoided. Foundayo in turn raises simvastatin, can make the pill less reliable for set windows, and may raise low-blood-sugar risk with insulin and sulfonylureas.
This guide draws on the Foundayo Summary of Product Characteristics (SmPC) and patient leaflet on the emc. It is information only, not medical advice: Foundayo is a prescription-only medicine, and a qualified prescriber decides whether it suits you alongside everything else you take.
Why Foundayo drug interactions happen
The SmPC says orforglipron is broken down mainly by a liver enzyme called CYP3A4, and it is also carried by transport proteins known as OATP1B. Blocking or speeding up those routes can change how much orforglipron is in your blood: more can make side effects likelier, less can make it work less well. Foundayo can also change other medicines' levels, or add to what they do. Our explainer on how orforglipron works covers the molecule itself.
The interactions at a glance
| Medicine group | What the UK label says | Examples |
|---|---|---|
| Strong CYP3A4 inhibitors | Foundayo maximum 9 mg | Clarithromycin, itraconazole, ketoconazole |
| Antivirals that block CYP3A4 and OATP1B | Avoid | Ritonavir, telaprevir |
| OATP1B inhibitors | Foundayo maximum 9 mg | Ciclosporin |
| Strong CYP3A4 inducers | Avoid | Rifampicin, carbamazepine, phenytoin, St John's wort |
| Moderate CYP3A4 inducers | Monitor effect; adjust dose | Bosentan, efavirenz |
| Statins | Halve simvastatin; caution with rosuvastatin above 20 mg | Simvastatin, rosuvastatin |
| The pill | Barrier or non-oral method for set windows | Oral hormonal contraceptives |
| Insulin and sulfonylureas | Low blood sugar risk; their dose may be lowered | Insulin, gliclazide |
| Blood pressure medicines | Low blood pressure more likely; dose may need changing | Any |
Medicines that raise Foundayo levels
In an SmPC study, the antibiotic clarithromycin raised total exposure to orforglipron about 3.5-fold. So with a strong CYP3A4 inhibitor, such as clarithromycin or the antifungals itraconazole and ketoconazole, the maximum Foundayo dose is 9 mg rather than 17.2 mg. The same limit applies with ciclosporin, which mainly blocks the OATP1B route and raised exposure about 2.6-fold. Two antivirals, ritonavir and telaprevir, block both CYP3A4 and OATP1B, and the SmPC says to avoid them.
Short courses are easy to overlook: if you are above 9 mg and are prescribed clarithromycin, the prescriber needs to know about Foundayo to decide on your dose. Our dosage page explains each strength.
Medicines that lower Foundayo levels
Some medicines speed up CYP3A4. With the epilepsy medicine carbamazepine, exposure fell by 82% in the SmPC's study. The label says to avoid strong CYP3A4 inducers because they may make Foundayo less effective, naming rifampicin (an antibiotic), carbamazepine and phenytoin (epilepsy medicines) and St John's wort. Moderate inducers, such as bosentan (for pulmonary hypertension) and the antiviral efavirenz, are not ruled out; the SmPC says to monitor whether Foundayo is still working and adjust the dose if needed.
Medicines Foundayo can affect
- Simvastatin. Foundayo raised the level of simvastatin's active form up to 2.5-fold, even when the statin was taken two hours later. The SmPC says to halve the simvastatin dose.
- Rosuvastatin. Levels rose about 1.7-fold at the top Foundayo dose; caution is advised above 20 mg of rosuvastatin.
- Oral topotecan. People taking this cancer medicine with Foundayo should be carefully monitored for side effects.
- Tablets in general. Foundayo slows stomach emptying, which can slow how quickly other tablets are absorbed; in one study, paracetamol's peak level was 28% lower. The effect is largest after the first dose and lessens over time, and based on modelling the SmPC does not expect a clinically relevant effect on commonly used medicines.
Foundayo and the contraceptive pill
The UK label says Foundayo may reduce how well oral hormonal contraceptives work. If you use the pill, it advises adding a barrier method such as condoms, or switching to a non-oral method such as an implant, injection or coil, for the 30 days after starting Foundayo and the 30 days after every dose increase.
Separately, the SmPC asks anyone who could become pregnant to use effective contraception throughout treatment. Foundayo should not be used in pregnancy or while breastfeeding, and should be stopped at least three weeks before a planned pregnancy.
Diabetes and blood pressure medicines
Foundayo is also licensed for type 2 diabetes. The SmPC says metformin and SGLT2 inhibitors (such as dapagliflozin) can be continued at their current dose.
Insulin and sulfonylureas, such as gliclazide, are different: with Foundayo they may raise the chance of low blood sugar, which the leaflet lists as very common with insulin and common with a sulfonylurea, against uncommon without either. Your prescriber may lower the insulin or sulfonylurea dose (the SmPC recommends cutting insulin in steps), and you will need to test your blood sugar as instructed. Warning signs include headache, drowsiness, weakness, dizziness, hunger, confusion, irritability, a fast heartbeat and sweating; avoid driving or using machines if you notice them.
Foundayo can also lower blood pressure, and the SmPC says this happened more often in people taking blood pressure medicines; the leaflet says their dose may need changing. Our side effects guide covers both effects.
Over-the-counter, herbal and supplement products
- St John's wort, the herbal remedy the leaflet names, should be avoided with Foundayo.
- Indigestion remedies. The proton pump inhibitor esomeprazole had no clinically meaningful effect on orforglipron, and the SmPC does not expect acid-reducing medicines in general to have one.
- Other herbal and "natural" products are not listed, which is not the same as being checked. Show a pharmacist the packet before starting one.
Tell every prescriber and pharmacist what you take
The leaflet asks you to tell your doctor or pharmacist about any medicine you are taking, have recently taken or might take. That includes your GP, hospital teams, dentist and pharmacist. Before an operation under general anaesthetic or deep sedation, tell that team too: the leaflet warns that the chance of food or liquid getting into the lungs may increase.
Foundayo carries the black triangle, meaning it is under additional monitoring. If you suspect a side effect, including from a combination of medicines, tell your prescriber or pharmacist and report it to the MHRA Yellow Card scheme.
Frequently asked questions
Can I take antibiotics while on Foundayo?
The UK label names two antibiotics, but its lists are examples, not complete. Clarithromycin raises orforglipron levels, so the SmPC limits Foundayo to 9 mg alongside it; rifampicin lowers them and should be avoided. Tell whoever prescribes the antibiotic that you take Foundayo.
Do I need extra contraception on Foundayo?
If you use the pill, yes, for set periods: a barrier method, or a switch to a non-oral method, for 30 days after starting and for 30 days after each dose increase. Effective contraception is advised throughout treatment.
Can Foundayo be taken with metformin?
The SmPC says metformin and SGLT2 inhibitors can be continued at their current dose. Insulin and sulfonylureas are handled differently because of the low blood sugar risk. Your prescriber decides the combination.
Is St John's wort safe with Foundayo?
No. The UK label says to avoid it, because it can lower orforglipron levels and may stop Foundayo working as well.
Do I need to space Foundayo apart from my other tablets?
No. Foundayo has no timing rule: one tablet a day at any time, with or without food, and the SmPC does not ask you to separate it from other medicines. In the SmPC's study, a two-hour gap did not help with simvastatin. Your other medicines' own instructions still apply.
More answers are on our FAQ page.
Sources
- Foundayo film-coated tablets — Summary of Product Characteristics (sections 4.2, 4.4, 4.5, 4.6 and 5.2). electronic medicines compendium (emc). medicines.org.uk
- Foundayo film-coated tablets — Patient Information Leaflet. electronic medicines compendium (emc). medicines.org.uk
- Medicines and Healthcare products Regulatory Agency. Yellow Card scheme. yellowcard.mhra.gov.uk