Switching from Mounjaro or Wegovy to Foundayo weight loss tablets safely

Can you switch from Mounjaro or Wegovy to Foundayo?

There is now direct clinical evidence for a particular type of transition: people who had completed long-term injectable tirzepatide or injectable semaglutide treatment and then moved to orforglipron for weight-loss maintenance. That evidence comes from the phase 3b ATTAIN-MAINTAIN trial. [3]

It does not mean everyone taking Mounjaro or Wegovy can follow the same transition. The people in the trial had completed 72 weeks of injectable treatment, had lost at least 5% of their body weight, and did not have diabetes. The trial therefore most closely reflects a maintenance situation after sustained treatment, rather than an early switch during dose escalation or a change made for every possible clinical reason. [3]

Foundayo is the UK brand name for orforglipron. The MHRA authorised it on 10 August 2026 for weight loss and weight maintenance in eligible adults, as well as for treatment of type 2 diabetes. It is a prescription-only medicine. [1]

Foundayo, not ‘Foundation’

If you searched for ‘switching from Mounjaro to Foundation’, ‘Foundation pill’ or ‘Foundation dosage’, the medicine referred to in this context is Foundayo. Foundayo is the licensed brand name for orforglipron in the UK. [1][2]

‘Foundation’ is not the medicine name, so we use Foundayo throughout the rest of this guide.

Mounjaro, Zepbound and tirzepatide: what is the difference?

Mounjaro contains tirzepatide and is a UK brand used for weight management and type 2 diabetes. Zepbound is a US tirzepatide brand. [5][6]

That matters for search wording. Someone looking for ‘switching from Zepbound to Foundayo’ is asking about the same active ingredient studied in the tirzepatide cohort of ATTAIN-MAINTAIN. For a UK reader, however, Mounjaro and tirzepatide are the clearer terms to use when discussing current UK treatment. [3][5][6]

What did ATTAIN-MAINTAIN actually study?

ATTAIN-MAINTAIN was a randomised, double-blind, placebo-controlled phase 3b trial at 29 sites in the United States. It included 376 adults who had completed SURMOUNT-5 and achieved at least 5% body-weight reduction after 72 weeks of injectable treatment. [3]

The study population is important. It did not test a person taking a low starter dose for a few weeks, someone changing because of every possible side effect or clinical problem, a person with type 2 diabetes, or someone taking oral Wegovy. [3]

What happened after switching from tirzepatide?

For the primary analysis, the researchers looked at participants whose body weight had plateaued by the end of SURMOUNT-5. At week 52, those assigned to orforglipron maintained an estimated 74.7% of the weight reduction they had achieved during SURMOUNT-5, compared with 49.2% among those assigned to placebo. [3]

A key secondary result looked at how many participants retained at least 80% of their previous weight reduction. In the tirzepatide cohort, this was 43.7% with orforglipron and 16.4% with placebo. [3]

These are group-level trial estimates, not predictions for an individual person. They also do not mean that everyone maintained exactly three-quarters of their previous loss.

What happened after switching from injectable Wegovy?

The semaglutide cohort showed the same broad direction of effect. Among participants whose weight had plateaued, those assigned to orforglipron maintained an estimated 79.3% of their previous weight reduction at week 52, compared with 37.6% with placebo. [3]

In the secondary threshold analysis, 55.0% of the orforglipron group maintained at least 80% of their previous weight reduction, compared with 6.9% of the placebo group. [3]

Again, these figures describe a specific trial population after long-term injectable semaglutide treatment. They should not be read as a promise of how much weight an individual will maintain after changing treatment.

Does this mean Foundayo is equivalent to staying on Mounjaro or Wegovy?

No. This is the most important limitation when interpreting the trial. ATTAIN-MAINTAIN compared orforglipron with placebo after participants stopped their previous injectable study treatment. There was no group that continued tirzepatide or semaglutide.

The trial therefore answers ‘what happened when people moved to orforglipron rather than placebo?’ much more directly than it answers ‘is changing to Foundayo as effective as staying on Mounjaro or Wegovy?’ The authors identify the missing continued-injectable comparator and the one-year study duration as limitations. [3]

There is another qualification. From week 24, participants assigned to placebo who regained at least 50% of the weight they had previously lost could receive rescue orforglipron. By week 52, only 31.3% of the tirzepatide-placebo group and 18.2% of the semaglutide-placebo group had completed treatment without receiving active therapy.

This was intended to limit the harm associated with substantial weight regain, but it means later comparisons are not a pure active-treatment-versus-untreated-placebo contrast. [3]

The strongest conclusion from ATTAIN-MAINTAIN is that orforglipron preserved more previous weight reduction than placebo after long-term injectable treatment. It does not establish equivalence to continuing the injectable medicine, nor does it identify the best maintenance strategy for every patient.

Alex Gibbins MPharm, IP, FRPharmS

What about switching from oral Wegovy to Foundayo?

ATTAIN-MAINTAIN does not provide direct evidence for this transition. Oral Wegovy is now authorised in the UK for weight management and contains semaglutide, but its pharmacokinetics and dosing are not interchangeable with the weekly injection.

Current UK product information specifically notes that the effect of switching between semaglutide tablets and injections cannot easily be predicted because oral semaglutide has greater variability in absorption. [4]

The semaglutide participants in ATTAIN-MAINTAIN had used injectable semaglutide 1.7mg or 2.4mg once weekly. The trial did not include people taking oral Wegovy before moving to orforglipron. A specific oral-Wegovy-to-Foundayo regimen should therefore not be inferred from the injectable evidence. [3][4]

What Foundayo dose is used when switching from Mounjaro, Zepbound or Wegovy?

There is no simple dose-equivalence table in current UK patient information. More importantly, the ATTAIN-MAINTAIN study protocol and the general UK Foundayo starting schedule are different. [2][3]

The researchers deliberately tested a higher transition dose in people with extensive prior injectable exposure to explore whether the usual escalation period could be shortened. The paper itself says this raises a question for further investigation; it does not turn that higher dose into a general rule for routine practice. [3]

The current UK PIL, by contrast, gives 0.8mg once daily as the general Foundayo starting dose, followed by clinician-directed increases no sooner than every 30 days, and tells patients not to change their dose unless instructed by their doctor. [2]

How soon after the last Mounjaro or Wegovy injection was Foundayo started in the trial?

ATTAIN-MAINTAIN aimed to give the first study dose within 14 days of the final SURMOUNT-5 injection. [3]

That timing describes how the study was run. The current UK Foundayo PIL does not state a general switching interval after tirzepatide or semaglutide. It should therefore not be turned into a rule such as ‘start Foundayo 14 days after your final injection’. [2][3]

What do we know about side effects during the studied transition?

During the first four weeks of ATTAIN-MAINTAIN, nausea, vomiting or diarrhoea were reported in 10.5% of the tirzepatide cohort and 9.5% of the semaglutide cohort. Most gastrointestinal adverse events were mild to moderate, and no dose de-escalations were required during those first four weeks.

Across both cohorts, discontinuation because of adverse events ranged from 4.8% to 7.3% among participants receiving the maximum tolerated orforglipron dose. [3]

This is useful tolerability evidence for the people who were actually studied. It is not evidence that switching will be easy for everyone, and it does not justify using the trial's higher starting dose without an individual prescribing decision.

Safety information that matters when changing treatment

Starting a different prescription medicine is not only a question of dose. The Foundayo PIL tells people to speak to a doctor, nurse or pharmacist before taking it if they have a history of pancreatitis, severe problems with stomach emptying, gallbladder problems, eye or vision problems, severe heart failure, or upcoming surgery under anaesthesia.

It also highlights dehydration risk with vomiting or diarrhoea and low blood sugar risk when Foundayo is used with insulin or a sulfonylurea. [2]

Tell your prescriber about all medicines and supplements you take. Foundayo has listed interactions with several medicines and with St John's wort, and the PIL gives specific advice for people using insulin, sulfonylureas and medicines for high blood pressure. [2]

The following symptoms need clear action rather than waiting to see whether they settle:

ATTAIN-MAINTAIN gives direct evidence that, in a selected group of adults who had completed 72 weeks of injectable tirzepatide or injectable semaglutide, moving to orforglipron maintained more of their previous weight reduction over the following year than moving to placebo. [3]

That is useful evidence for maintenance after long-term injectable treatment. It is not a universal switching protocol. The study did not include oral Wegovy switchers or people with diabetes, did not compare Foundayo with continuing Mounjaro or Wegovy, and used a transition regimen that differs from the general starting schedule in current UK Foundayo patient information. [2][3][4]

For those reasons, the evidence can inform a conversation with a prescriber, but it cannot tell an individual reader which dose to start, how long to wait after a final injection, whether treatments should overlap, or whether changing medicine is the right option for them.