Switching from Mounjaro to Foundayo (Orforglipron) : What the Evidence Actually Shows
Foundayo (orforglipron) was licensed by the MHRA on 10 August 2026, and the question that followed almost immediately from people already on injections was whether they could move across to a daily tablet. The answer is yes, in principle — but it is a clinical decision rather than a straight swap, and the trial evidence points somewhere more specific than most coverage suggests. Mounjaro (tirzepatide) and Foundayo are different medicines with different mechanisms, and the honest position is that switching mid-way through active weight loss is likely to slow your progress.
Quick verdictSwitching from Mounjaro to Foundayo is possible, and the strongest evidence supports it as a maintenance option after weight has plateaued rather than as a way to keep losing weight.
In the ATTAIN-MAINTAIN trial, participants switching from tirzepatide maintained approximately 74.7% of their previous weight reduction at week 52. Those switching from semaglutide maintained 79.3%. In kilogram terms, the tirzepatide group was around 5 kg heavier than at the point of switching, and the semaglutide group around 1 kg.
The trial’s primary endpoint was the percentage of previous reduction maintained, not kilograms regained. Individual responses varied considerably, so these are study-group averages rather than a prediction of what any one person will experience.
There is no milligram-for-milligram conversion from Mounjaro to Foundayo. Notably, ATTAIN-MAINTAIN did not restart participants at the bottom of the Foundayo ladder — it moved them directly to a higher transition dose. Your starting dose is a prescriber decision based on the UK product information and your recent treatment history.
About the authorShadeia Younis is the founder and Superintendent Pharmacist of Slinic (GPhC No. 2052119), with 25 years of clinical pharmacy experience. She has owned and operated community pharmacies in Lancashire since 2008, oversees the clinical governance of Slinic’s prescribing service, and holds SCOPE certification in obesity management. She has been recognised as a finalist or winner across 19 national and European awards spanning healthcare and business, including Independent Pharmacy Awards’ Independent Pharmacist of the Year.
Sources usedMHRA authorisation information, 10 August 2026 · Manufacturer prescribing information for Foundayo (orforglipron) · UK Summary of Product Characteristics (Mounjaro KwikPen) · ATTAIN-1 (Wharton et al, NEJM 2025) · ATTAIN-MAINTAIN (Aronne et al, Nature Medicine 2026) · SURMOUNT-1, -4 and -5 peer-reviewed publications · NICE TA1026. Full list in the references at the end of this guide.
The UK Summary of Product Characteristics for Foundayo was published on the electronic Medicines Compendium on 14 August 2026 and has been used throughout. Foundayo carries a black triangle (▼), meaning it is subject to additional monitoring — report any suspected adverse reaction via the MHRA Yellow Card scheme.
ImportantFoundayo (orforglipron) and Mounjaro (tirzepatide) are prescription-only medicines. This guide is general information and does not replace advice from a qualified healthcare professional. Treatment is supplied only after an individual clinical assessment by a UK-registered prescriber, and is not suitable for everyone. Never stop, start or change a prescribed medicine without speaking to your prescriber first.
If you experience severe abdominal pain, persistent vomiting, breathing difficulty, facial swelling or signs of an allergic reaction, seek urgent medical advice or contact emergency services immediately.
A note on sources: Foundayo was authorised in the UK on 10 August 2026, and the UK Summary of Product Characteristics was published on 14 August 2026. Dosing, interactions, contraception, missed doses and pregnancy advice on this page follow the UK SmPC. Foundayo carries a black triangle (▼) — it is under additional monitoring, and any suspected side effect should be reported through the MHRA Yellow Card scheme.
Mounjaro and Foundayo at a glance
| Mounjaro | Foundayo | |
|---|---|---|
| Active ingredient | Tirzepatide | Orforglipron |
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist only (small molecule, non-peptide) |
| How it is taken | Once-weekly subcutaneous injection | Once-daily tablet, swallowed whole |
| Food and water | Any time, with or without food | Any time, with or without food, no water restriction |
| Starting dose | 2.5 mg weekly | 0.8 mg daily |
| Maximum dose | 15 mg weekly | 17.2 mg daily |
| Titration interval | Minimum 4 weeks per step | Minimum 30 days per step |
| Storage | Refrigerated 2–8°C before first use | Room temperature, protected from light |
| UK licensing | Licensed for weight management and type 2 diabetes | Licensed 10 August 2026 for weight management and type 2 diabetes |
| Legal status | Prescription-only medicine | Prescription-only medicine |
| NHS availability | Yes, phased and tightly restricted | Not currently — NICE decision pending |
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Foundayo is not “oral Mounjaro”
This is the single most common misunderstanding about the switch, and it is the one that leads to disappointment afterwards.
Both medicines are made by Eli Lilly and both involve GLP-1 receptor agonism, but they are different medicines with different active ingredients and mechanisms.
Mounjaro contains tirzepatide, which acts on two receptors — GIP and GLP-1. The dual mechanism is a substantial part of why it produces the results it does. Our full Mounjaro UK guide covers how this works in detail.
Foundayo contains orforglipron, which acts on GLP-1 receptors only. It is also a different kind of molecule altogether — a small-molecule, non-peptide agonist, which is precisely why it survives digestion and can be given as a tablet rather than an injection. Our full Foundayo guide covers the doses, evidence and side effects in detail.
Anyone describing Foundayo as the tablet version of your current injection is wrong, and the distinction directly determines what you should expect from a switch.
It is also not the Wegovy pillThe Wegovy pill is oral semaglutide, and it comes with a fasting window and a water restriction on dosing. Foundayo has neither — it can be taken at any time of day, with or without food. If the reason you want a tablet is convenience, that difference is worth knowing before you choose between them.
The efficacy difference is real, and it is not small
Most provider pages soften this. It should be stated plainly, because it is the deciding factor for anyone still actively losing weight.
In ATTAIN-1, the main phase 3 trial of orforglipron in 3,127 adults with obesity and without diabetes, mean weight reduction at 72 weeks was 12.4% at the highest dose against 0.9% with placebo — a difference of 11.5 percentage points. Around 12.4 kg was lost on average at that dose. Just under 60% of participants on the highest dose lost 10% or more of their body weight, and 20.1% lost 20% or more.
Expressed against the marketed tablet strengths you would actually be prescribed, the UK SmPC reports these average 72-week reductions.
| Foundayo tablet strength | Trial capsule equivalent | Average weight reduction at 72 weeks |
|---|---|---|
| 5.5 mg | 6 mg | 7.8% |
| 9 mg | 12 mg | 9.3% |
| 17.2 mg | 36 mg | 12.4% |
For comparison, SURMOUNT-1 studied tirzepatide over the same 72-week period and found mean reduction of approximately 15% at 5 mg, 19.5% at 10 mg and 20.9% at 15 mg, against 3.1% with placebo.
| Medicine | Highest dose | Mean weight reduction at 72 weeks |
|---|---|---|
| Foundayo (orforglipron) | 17.2 mg daily | 12.4% |
| Mounjaro (tirzepatide) | 15 mg weekly | Approximately 21% |
No head-to-head trial has compared the two directly. These are separate studies with different populations and protocols, so the exact size of the gap is imprecise — but the direction of it is not in doubt.
A number almost everyone is quoting wronglyThe ATTAIN-1 trial used orforglipron capsules at 6 mg, 12 mg and 36 mg. The marketed Foundayo tablet strengths are 0.8 mg to 17.2 mg. These are not the same scale. The published mapping is: capsule 1 / 3 / 6 / 12 / 24 / 36 mg corresponds to tablet 0.8 / 2.5 / 5.5 / 9 / 14.5 / 17.2 mg.
If you see a page claiming Foundayo’s maximum dose is 36 mg, or comparing a 36 mg Foundayo dose against Mounjaro’s 15 mg, it has confused trial capsules with marketed tablets. The maximum licensed daily dose is 17.2 mg.
What this means in practice: if you are still losing weight on Mounjaro and tolerating it well, switching to Foundayo is likely to slow your progress. Convenience, needle avoidance and travel are legitimate reasons to switch. Expecting better results is not.
What the switching evidence actually shows
There is one trial that directly answers this question, and it is worth understanding properly because it is the entire evidence base for the switch.
ATTAIN-MAINTAIN was a 52-week, randomised, double-blind, placebo-controlled phase 3b trial. It enrolled 376 adults who had already completed 72 weeks of treatment with tirzepatide or semaglutide in the SURMOUNT-5 trial and had reached a weight plateau, defined as less than 5% weight change between weeks 60 and 72. They were re-randomised in a 3:2 ratio to either orforglipron or placebo.
The trial did not restart people at the bottom of the ladderThis is the detail most coverage misses. Participants moved directly onto a 12 mg investigational capsule — corresponding to the 9 mg marketed tablet — ideally within 14 days of their last injection, rather than beginning at the 0.8 mg initiation dose used in people new to the medicine. That transition was generally well tolerated.
The authors note this raises the possibility of moving established injectable users directly to higher orforglipron doses, while stating that further research is required. It does not by itself establish UK licensed switching practice — the UK product information and your prescriber’s judgement govern that.
The results
| Previous injection | Participants | Previous reduction maintained (primary endpoint) | Weight at week 52 vs switch point |
|---|---|---|---|
| Tirzepatide (Mounjaro) | 205 | Approximately 74.7% | Approximately 5 kg heavier |
| Semaglutide (Wegovy) | 171 | 79.3% | Approximately 1 kg heavier |
Alongside the weight outcome, participants held much of the accompanying improvement in waist circumference, blood pressure, blood sugar, triglycerides and cholesterol. In the semaglutide cohort, orforglipron maintained 79.3% of the prior weight reduction against 37.6% on placebo among those whose weight had plateaued.
What this means if you are on MounjaroThere is a consistent gap between the two cohorts. Participants coming from tirzepatide maintained approximately 74.7% of their previous reduction; those from semaglutide, 79.3%.
This is not a flaw in the trial. It reflects that tirzepatide produces greater weight loss in the first place, so moving to a single-receptor medicine represents a larger step down.
The trial therefore suggests that some weight regain may occur after transitioning from tirzepatide to orforglipron, although individual responses varied and the study does not allow us to predict what will happen to an individual patient.
Switching preserved substantially more of the previous weight reduction than assignment to placebo, although interpretation after week 24 is complicated by rescue orforglipron being offered to participants who regained 50% or more of their earlier loss.
What the trial does not tell you
It studied people who had already plateaued. Everyone in ATTAIN-MAINTAIN had completed 72 weeks of injectable treatment and reached a stable weight. The evidence for switching during ongoing active weight loss is far less established than the evidence for switching after weight has plateaued.
It was conducted entirely in the United States, across 29 sites, in a predominantly white population. The authors flag both as limitations. UK prescribing practice is governed by the UK product information, not by a US trial protocol.
The placebo comparison weakens after week 24, because participants who regained 50% or more of their previous loss could be given rescue orforglipron. The authors identify this as a limitation on interpreting the later placebo data.
It ran for 52 weeks. What happens over several years is not yet known.
It was sponsored by the manufacturer of both medicines involved, which is normal for trials of this kind but worth stating.
Who might reasonably consider switching
- You have reached your goal weight on Mounjaro and want to come off injections without losing most of what you have achieved
- You have a genuine needle phobia that is affecting how consistently you take treatment
- You travel frequently and find the refrigeration requirement and weekly schedule difficult — Foundayo is stored at room temperature
- Injection-site reactions have been a persistent problem
- You have plateaued on Mounjaro and want to discuss alternatives with a prescriber
- A daily routine genuinely suits you better than a weekly one
Who may be less suited to switching
- You are mid-way through active weight loss and progressing well
- You are tolerating Mounjaro without significant side effects
- You are switching because you have read that the tablet works better — the trial evidence does not support that
- You are achieving good weight-management outcomes on tirzepatide and have no clinical or practical reason to change treatment
- You take a medicine that interacts with orforglipron and has not yet been reviewed
- You have not discussed it with a prescriber
Neither list replaces an individual assessment. They are a starting point for that conversation, not a substitute for it.
Every change of treatment is reviewed by a prescriber first
Slinic does not move patients between medicines on request. A UK-registered prescriber reviews your treatment history, current dose and full medication list before any decision, and may conclude that a change is not appropriate.
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How a switch actually works
There is no published UK switching protocol for Mounjaro to Foundayo. The medicine was authorised on 10 August 2026 and clinical practice will develop over the coming months. What follows is what is known now.
There is no milligram-for-milligram conversion
Your Mounjaro dose does not translate into a Foundayo dose. The two medicines are on entirely different scales and act on different receptors, so no conversion table exists or could exist.
Standard Foundayo dosing begins at 0.8 mg once daily for at least 30 days. Whether that applies to someone transitioning off an injection is a different question, and not one that current UK guidance settles. ATTAIN-MAINTAIN transitioned established injectable users directly onto a 12 mg investigational capsule — equivalent to the 9 mg marketed tablet — and reported it as generally well tolerated. The authors framed this as raising the possibility of higher transition doses, while stating that further research is required.
That is trial evidence, not an accepted UK switching dose. The appropriate starting dose after injectable GLP-1 treatment should be decided by the prescriber, using the applicable UK product information and your recent treatment history. Do not use the trial protocol to select your own starting dose.
Do not take both concurrently
Do not take Mounjaro and Foundayo at the same time unless specifically instructed under an authorised clinical protocol. Switching requires a prescriber-defined interval between your final injection and your first tablet.
Worth understanding: tirzepatide remains pharmacologically active for a period after the last injection, so some overlap in the body is unavoidable in any switch — ATTAIN-MAINTAIN deliberately started the tablet within 14 days precisely to limit the gap. The point is that you should not be deliberately dosing both medicines, not that the two can never coexist in your system.
Expect some reduction in effect during the transition
How much depends entirely on the starting dose your prescriber sets and how quickly you titrate from there. A transition beginning at a higher dose narrows this window considerably compared with starting from the bottom. Either way, plan for a period when appetite suppression feels different from what you are used to, rather than being caught out by it.
Your other medicines need reviewing first
Orforglipron interacts with more medicines than tirzepatide does, and this is genuinely the step most likely to change the answer. See the section on other medicines below.
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Foundayo dose ladder
| Step | Daily dose | Minimum time before increasing | Purpose |
|---|---|---|---|
| Starting dose | 0.8 mg | 30 days | Introduces treatment gradually |
| Step 2 | 2.5 mg | 30 days | Continued titration |
| Step 3 | 5.5 mg | 30 days | Lowest recognised maintenance dose |
| Step 4 | 9 mg | 30 days | Maintenance option; also the ceiling for certain drug interactions |
| Step 5 | 14.5 mg | 30 days | Maintenance option |
| Maximum | 17.2 mg | — | Maximum licensed daily dose |
This is the standard initiation schedule, not a validated Mounjaro-to-Foundayo conversion scheduleStandard Foundayo dosing begins at 0.8 mg once daily for at least 30 days. However, ATTAIN-MAINTAIN transitioned established injectable users directly to a 12 mg investigational capsule, equivalent to the 9 mg marketed tablet, and this was generally well tolerated.
The authors said this raises the possibility of higher transition doses, but that further research is required. Patients should therefore not use the trial protocol to select their own starting dose. Treatment should follow the applicable UK product information and prescriber judgement.
Increases from 5.5 mg onwards are based on your response and how well you are tolerating the current dose, not on a fixed schedule. Thirty days is the earliest, not a target. Staying longer at a dose is a legitimate clinical decision, and remaining at 5.5 mg or 9 mg indefinitely is perfectly reasonable if it is working for you.
Taking the tabletSwallow tablets whole — do not break, crush or chew them. One tablet per day, at any time of day, with or without food and with no water restriction. If a dose is missed, resume dosing as soon as possible. Never take more than one tablet in a day, and never double up to make up for a missed dose or to reach a higher dose.
Follow the patient information leaflet supplied with your medicine and your prescriber’s directions.
Your first weeks after switching
| Period | What is commonly experienced | What to do |
|---|---|---|
| Between medicines | Appetite begins returning as tirzepatide clears. Some people find this the hardest part of the process. | Hold your eating patterns deliberately rather than relying on the medicine. This is where habits built during treatment earn their keep. |
| First tablet | Gastric emptying is slowed most after the very first dose, and the effect diminishes over time. Mild nausea is common. | Smaller portions, keep fluids up. Take the tablet whole, at a time you will remember. |
| First month | The degree of appetite effect during transition may vary according to the dose selected, previous treatment exposure and individual response. | Report tolerance honestly. Do not increase on your own. |
| Subsequent increases | Nausea may briefly return after each step up before settling. | Staying longer at a dose is a legitimate option if symptoms are significant. |
| Settling | Most people find a dose that balances effect against tolerance. | Higher is not automatically better. The aim is the lowest dose that works for you. |
A potential switching mistakeJudging the tablet too early. Depending on the dose you start at and how quickly you titrate, the effect during the transition period may not resemble the maintenance dose of Mounjaro you were on. Those are not comparable things, and an early impression is not a fair test of the medicine.
Side effects compared
Both medicines share the GLP-1 class side-effect profile, which is predominantly gastrointestinal. In the phase 3 weight management studies, gastrointestinal effects occurred in 68.7% of participants at the highest dose against 36.3% on placebo, and were mostly mild (61.8%) or moderate (34.3%). Discontinuation because of gastrointestinal effects occurred in 6.8% at the highest dose against 0.6% on placebo.
| Side effect | Practical self-care | When to contact a clinician |
|---|---|---|
| Nausea | Smaller portions, eat slowly, avoid rich and fatty meals, plain foods if better tolerated | Persistent, preventing you eating or drinking, or not settling after several weeks |
| Diarrhoea | Maintain fluid intake, avoid known triggers | Severe, prolonged, or with signs of dehydration |
| Constipation | Hydration, gradual increase in fibre, stay active where possible | No bowel movement for several days, or with pain or bloating |
| Vomiting | Small frequent sips of fluid, do not force food | Persistent, unable to keep fluids down, or with abdominal pain |
| Abdominal discomfort | Smaller portions, note any pattern | Severe or persistent pain, particularly radiating to the back — seek urgent advice |
| Reduced appetite | Prioritise protein and nutrient density in what you do eat | If intake falls so low you cannot meet basic nutritional needs |
What changes when you switch
No injection-site reactions. The most obvious gain, and for some people the whole reason for switching.
The pattern may feel different. The experience of a once-daily tablet compared with a once-weekly injection may feel different, though there is no comparative clinical evidence establishing how. Gastrointestinal adverse effects remain the most commonly reported side effects with orforglipron, and in ATTAIN-MAINTAIN they were mostly mild to moderate.
A different interaction profile. Orforglipron is metabolised via CYP3A4, which brings interactions Mounjaro does not have. Covered below.
Seek urgent medical help for
- Severe abdominal pain, particularly if persistent or radiating to the back — this can indicate pancreatitis
- Swelling of the face, lips, tongue or throat, or difficulty breathing
- Pain in the upper right abdomen, yellowing of the skin or eyes, or pale stools — acute gallbladder disease has been reported with orforglipron in clinical trials
- Persistent vomiting with severe abdominal pain and inability to pass stool or wind
- Symptoms of severe dehydration: confusion, fainting, unable to keep any fluid down
Other medicines: the step most likely to change the answer
This section deserves more attention than it usually gets, because orforglipron has a broader interaction profile than tirzepatide and this is where a switch is most likely to be ruled out.
Bring your full medication list to the assessmentOrforglipron is a substrate of CYP3A4 and CYP2J2, and of P-gp, OATP1B1 and OATP1B3. That gives it a wider interaction profile than tirzepatide, and it is the most likely single reason a prescriber concludes a switch is not appropriate. Bring everything — prescriptions, over-the-counter medicines, herbal products and supplements.
Strong CYP3A4 inhibitors — ketoconazole, clarithromycin, itraconazole. Clarithromycin raised orforglipron exposure 3.5-fold in study. Your maximum Foundayo dose is capped at 9 mg daily, below the licensed maximum.
Strong CYP3A4 inhibitors that also inhibit OATP1B — ritonavir and telaprevir. These should be avoided altogether.
OATP1B inhibitors such as ciclosporin also cap the dose at 9 mg daily.
Strong CYP3A4 inducers — rifampicin, phenytoin, carbamazepine and St John’s wort. Carbamazepine cut orforglipron exposure by 82%. Concomitant use should be avoided.
Moderate CYP3A4 inducers such as bosentan and efavirenz may also reduce effectiveness. Response should be monitored and the dose adjusted as needed.
Simvastatin. The simvastatin dose should be halved when taken with orforglipron — exposure to its active metabolite rose up to 2.5-fold in study. This applies whether the two are taken together or the statin is taken two hours later.
Rosuvastatin. Caution is advised above 20 mg. No adjustment is needed at lower doses.
Oral medicines generally. Orforglipron delays gastric emptying, which can affect how other tablets are absorbed. The delay is largest after the first dose and diminishes over time. This matters most for medicines where timing or a narrow therapeutic range is important.
Insulin and sulfonylureas. Hypoglycaemia risk rises substantially in combination — reported in 6.7% of trial patients taking a sulfonylurea against 0.5% of those not. Your diabetes team may reduce these doses, and blood glucose self-monitoring is needed. Metformin and SGLT2 inhibitors can usually continue unchanged.
Other GLP-1 medicines. Never combine.
Bring your full medication list to the assessmentIncluding anything over the counter, herbal or supplemental. This is not a formality on a switch — it is the specific thing that determines whether Foundayo is a sensible option for you, and it is the reason a straight swap on request is not something a responsible prescriber will do.
Contraception and pregnancy
This is the section to read most carefully if you take the pill, because the UK SmPC gives specific instructions and they are easy to get wrong.
Orforglipron may reduce the effectiveness of oral hormonal contraceptives. If you use one, the UK product information advises switching to a non-oral method of contraception, or adding a barrier method, for 30 days after starting Foundayo and for 30 days after every dose increase.
That second part matters and is often missed. It is not a one-off precaution at the start of treatment — it applies again at each step up the dose ladder. With five possible increases, that is potentially several separate 30-day windows over the course of treatment.
Women of childbearing potential should use effective contraception throughout treatment. Plan each 30-day window before the dose increase rather than afterwards.
Foundayo should not be used in pregnancy. Because of how long orforglipron stays in the body, the UK SmPC advises stopping it at least three weeks before a planned pregnancy. If you become pregnant while taking it, stop and contact your prescriber straight away. It should not be used while breastfeeding either.
Practical differences that people underestimate
| Mounjaro | Foundayo | |
|---|---|---|
| Storage | Fridge at 2–8°C before first use, then up to 30 days at up to 30°C | Room temperature, protected from light, in the original bottle and carton |
| Travel | Cool bag, hand luggage, never frozen, never above 30°C | No cold chain to manage |
| Consumables | Needles, swabs, sharps bin | None |
| Routine | Once weekly, same day | Once daily — easier to forget, harder to skip unnoticed |
| Missing a dose | Under 4 days, take it; over 4 days, skip it | Resume as soon as possible, never more than one tablet a day |
The storage and travel difference is a genuine advantage and one of the better reasons to switch. The daily routine cuts both ways: some people find a tablet with breakfast far easier to sustain than a weekly injection, while others find weekly adherence simpler precisely because it is a deliberate event.
Cost
Foundayo pricing in the UK is still settling. Prices published in the first weeks after authorisation are provisional, several providers have not published a figure at all, and some bundle coaching or programme fees into the monthly cost while others charge them separately.
Compare on twelve-month totals at the dose you are likely to reach, including delivery and any consultation charges, rather than on a starting-dose headline. That advice applies to both medicines equally.
Our complete UK guide to Foundayo covers what is known about pricing across providers as it develops.
Availability and NHS access
Foundayo was authorised by the MHRA on 10 August 2026, making the UK the first country in Europe to license orforglipron for weight management and type 2 diabetes.
Authorisation and availability are different things. A newly licensed medicine typically takes several weeks to reach the supply chain — the Wegovy pill followed the same pattern earlier in 2026.
It is not currently available on the NHS. NHS funding is a separate decision made by NICE and that assessment is underway, with an outcome expected later in 2026. Mounjaro, by contrast, is already available on the NHS through a phased programme, though access remains tightly restricted. Our Mounjaro UK guide covers the current cohort criteria.
Common switching mistakes
- Expecting to keep losing weight. The evidence supports maintenance, not continued loss.
- Assuming your Mounjaro dose transfers. There is no conversion between the two — but equally, do not assume you must restart at the very bottom. Your prescriber sets the dose.
- Deliberately dosing both medicines. Not without an authorised clinical protocol.
- Choosing your own starting dose from something you have read, including from the trial protocol.
- Skipping titration steps to catch up. Produces side effects without benefit.
- Not disclosing every medicine. The CYP3A4 interactions are the specific reason this matters more here.
- Switching mid-loss because a tablet sounds easier. The convenience is real; the trade-off is real too.
- Treating the gap between medicines as a holiday. Appetite returns during it.
- Crushing or splitting tablets. They must be swallowed whole.
- Sourcing outside the regulated supply chain. The most dangerous item on this list, and demand for a newly launched medicine is exactly when counterfeit supply appears.
Myths about switching
| Claim | Reality |
|---|---|
| “Foundayo is oral Mounjaro” | Different active ingredient and different mechanism. Mounjaro acts on two receptors, Foundayo on one. Same manufacturer, different medicine. |
| “You won’t regain any weight” | In ATTAIN-MAINTAIN, participants coming from tirzepatide were around 5 kg heavier at 52 weeks than at their switch point, maintaining roughly 74.7% of the prior reduction. Not 100%. |
| “The maximum dose is 36 mg” | That was the trial capsule dose. The maximum licensed tablet dose is 17.2 mg daily, and the two are equivalent. |
| “A tablet must be gentler” | The side-effect profile is the same GLP-1 class profile. It arrives daily rather than weekly, which is different, not gentler. |
| “Everyone restarts at 0.8 mg” | That is the initiation dose for people new to a GLP-1. ATTAIN-MAINTAIN moved established injectable users directly to a much higher dose. Your prescriber decides. |
| “You can switch straight across at the same dose” | There is no milligram-for-milligram conversion between tirzepatide and orforglipron. The dose is set clinically, not by arithmetic. |
| “Switching is a way to take a break from treatment” | Obesity is a chronic condition. A switch is a change of treatment, not a pause in it. |
Frequently asked questions
1. Can I switch from Mounjaro to Foundayo?
Yes, in principle, but it requires prescriber oversight. There is no milligram-for-milligram conversion, you should not deliberately take the two medicines concurrently, and your other medicines need reviewing first.
2. Will I lose more weight on Foundayo?
No. In separate trials, tirzepatide produced mean reduction of around 21% at 15 mg over 72 weeks against approximately 11% for orforglipron at its highest dose. Foundayo’s advantage is that it is a daily tablet, not that it works better.
3. Will I regain weight if I switch?
Some regain is likely. In ATTAIN-MAINTAIN, participants transitioning from tirzepatide were around 5 kg heavier after 52 weeks than at the point of switching, maintaining approximately 74.7% of their previous weight reduction. Those coming from semaglutide were around 1 kg heavier, maintaining 79.3%. Individual responses varied considerably, so these are study-group averages rather than a prediction for any one person.
4. Is Foundayo just Mounjaro in tablet form?
No. Different active ingredient, different mechanism. Mounjaro’s tirzepatide acts on GIP and GLP-1 receptors; Foundayo’s orforglipron acts on GLP-1 only.
5. What dose of Foundayo would I start on?
There is no simple conversion from your Mounjaro dose. Standard Foundayo dosing begins at 0.8 mg once daily for at least 30 days. ATTAIN-MAINTAIN transitioned established injectable users directly onto a dose equivalent to the 9 mg tablet, but the authors described that as warranting further research rather than as established practice. Your prescriber decides, using the applicable UK product information and your recent treatment history.
6. How long until I reach an effective dose?
That depends on where your prescriber starts you. A higher transition dose shortens the process considerably compared with beginning at the bottom of the initiation ladder.
7. Can I take both while I transition?
Do not take Mounjaro and Foundayo concurrently unless specifically instructed under an authorised clinical protocol. A switch requires a prescriber-defined interval between the final injection and the first tablet.
8. How long after my last Mounjaro injection can I start?
Your prescriber will advise. Tirzepatide remains pharmacologically active for a period after the final dose. In ATTAIN-MAINTAIN the first tablet was ideally given within 14 days of the last injection, but that was a trial protocol and does not set UK prescribing practice.
9. Will my appetite come back in between?
To some degree, and the size of that window depends on your transition dose. Plan for it rather than being caught out by it.
10. Do I need to fast before taking Foundayo?
No. Unlike the Wegovy pill, Foundayo has no fasting window and no water restriction. It can be taken at any time of day, with or without food.
11. Can I crush or split the tablet?
No. Tablets must be swallowed whole.
12. What if I miss a dose?
Resume dosing as soon as possible. Never take more than one tablet in a day, and do not double up to compensate. If you have missed a long stretch of doses, speak to your prescriber before restarting.
13. Does Foundayo need to be kept in the fridge?
No, and this is one of its real practical advantages over Mounjaro. Store at room temperature, protected from light, in the original bottle and carton.
14. Are the side effects the same?
Broadly the same GLP-1 class profile, predominantly gastrointestinal — nausea, constipation, diarrhoea, vomiting, dyspepsia and abdominal pain are all listed as very common. Injection-site reactions obviously stop.
15. Does Foundayo interact with more medicines than Mounjaro?
Yes. Orforglipron is a substrate of CYP3A4 and CYP2J2, and of P-gp, OATP1B1 and OATP1B3. Strong CYP3A4 inhibitors and OATP1B inhibitors cap the dose at 9 mg daily, strong inducers should be avoided, and the simvastatin dose must be halved alongside it. It also delays gastric emptying, which can affect absorption of other tablets.
16. Is Foundayo available on the NHS?
Not currently. A NICE decision is expected later in 2026.
17. Can I switch back to Mounjaro if it doesn’t suit me?
This would again be a prescriber decision, and restarting Mounjaro after a break may mean restarting at a lower dose than you previously took. See our guide on restarting Mounjaro after a break.
18. Is switching a good idea?
That depends on your circumstances and is a question for your prescriber rather than a webpage. What can be said generally: the evidence for switching during ongoing active weight loss is much less established than the evidence for switching after weight has plateaued. ATTAIN-MAINTAIN studied only the latter group.
Summary
Switching from Mounjaro to Foundayo is clinically possible and has a genuine evidence base behind it — but that evidence supports it as a maintenance route after weight loss, not as a way to continue losing.
If you are on Mounjaro specifically, the trial average is instructive: participants transitioning from tirzepatide were around 5 kg heavier a year later than at their switch point, maintaining roughly three-quarters of what they had lost. Individual responses varied considerably, so that is context for a conversation rather than a forecast.
Practically, there is no conversion from your Mounjaro dose — your prescriber sets a starting point, and it may be considerably higher than the initiation dose used in people new to a GLP-1. The two medicines should not be deliberately taken together, and your other prescriptions need reviewing because orforglipron interacts with more of them than tirzepatide does. None of that is a reason not to switch. All of it is a reason to do it with a prescriber rather than on your own.
Talk it through with a UK-registered prescriber
Whether a change of treatment is clinically appropriate depends on your history, your current dose and the other medicines you take. Slinic is a GPhC-registered, NHS-contracted pharmacy providing clinician-led weight management with monthly reviews included.
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Related guides
- Foundayo (Orforglipron) UK — the complete guide to the oral GLP-1 tablet.
- Mounjaro UK — costs, eligibility, doses and side effects.
- Wegovy Pill UK — how oral semaglutide compares.
- Weight Loss Injections UK — the full overview of treatment options.
- Mounjaro vs Wegovy — comparing the two injections.
- Cheapest Mounjaro UK 2026 — every provider compared.
- Mounjaro Side Effects Guide — symptom-by-symptom management.
- Restarting Mounjaro After a Break — safe reordering guide.
- Mounjaro Dosing Schedule — full titration guide.
- Slinic Weight Loss Clinic — start an assessment.
References
- MHRA — Foundayo (orforglipron) marketing authorisation, 10 August 2026. products.mhra.gov.uk
- electronic Medicines Compendium — Foundayo 17.2 mg film-coated tablets, Summary of Product Characteristics, Eli Lilly and Company Limited. Last updated on emc 14 August 2026. medicines.org.uk/emc/product/102532/smpc
- electronic Medicines Compendium — Mounjaro KwikPen Summary of Product Characteristics. medicines.org.uk/emc
- Wharton S, et al. Orforglipron, an Oral Small-Molecule GLP-1 Receptor Agonist for Obesity Treatment. N Engl J Med. 2025;393:1796–1806. doi:10.1056/NEJMoa2511774
- Aronne LJ, et al. Orforglipron for maintenance of body weight reduction: the double-blind, randomized phase 3b ATTAIN-MAINTAIN trial. Nat Med. 2026. doi:10.1038/s41591-026-04386-7
- Jastreboff AM, et al; SURMOUNT-1 Investigators. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216. doi:10.1056/NEJMoa2206038
- Aronne LJ, et al; SURMOUNT-4 Investigators. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity. JAMA. 2024;331(1):38–48. doi:10.1001/jama.2023.24945
- Aronne LJ, et al; SURMOUNT-5 Trial Investigators. Tirzepatide as compared with semaglutide for the treatment of obesity. N Engl J Med. 2025.
- NICE TA1026 — Tirzepatide for managing overweight and obesity. nice.org.uk/guidance/ta1026
- NICE NG246 — Overweight and obesity management. nice.org.uk/guidance/ng246
