Foundayo vs Mounjaro: Differences between the weight loss medications

Foundayo vs Mounjaro at a glance

Foundayo was authorised by the MHRA on 10 August 2026, and its UK Patient Information Leaflet was published on emc on 12 August 2026.[1][6] The dosing and administration information above comes from that leaflet and the current Mounjaro Summary of Product Characteristics.[1][2] The milligram figures should not be compared with each other: 17.2mg of Foundayo is not automatically “stronger” than 15mg of Mounjaro because the number is larger. They are different medicines with different formulations and dosing schedules.

Is Foundayo the same as Mounjaro?

Foundayo and Mounjaro are different medicines. Foundayo contains orforglipron, a small-molecule, non-peptide GLP-1 receptor agonist taken by mouth. Mounjaro contains tirzepatide, a medicine that activates both GIP and GLP-1 receptors and is given by subcutaneous injection.[1][2][3]

Both are made by Eli Lilly, but that does not make Foundayo an oral version of Mounjaro. The active ingredients, receptor activity, formulation, dosing schedule and clinical evidence are different.[1][2] So the common search question “is Foundayo Mounjaro in pill form?” has a simple answer: no.

How do Foundayo and Mounjaro work differently?

Foundayo’s active ingredient, orforglipron, activates the GLP-1 receptor. The UK patient leaflet explains that Foundayo influences appetite regulation, which may help people eat less and reduce body weight.[1]

Mounjaro’s active ingredient, tirzepatide, activates both GIP and GLP-1 receptors. Its UK product information describes effects on appetite, satiety, hunger and food cravings.[2]

That gives a clear mechanistic distinction:

• Foundayo: GLP-1 receptor agonist.
• Mounjaro: dual GIP and GLP-1 receptor agonist.

It would be a mistake, however, to use that difference alone to explain the gap between their weight-loss trial results. ATTAIN-1 and SURMOUNT-1 were separate studies. They did not test whether activating two receptor systems rather than one was the reason for the difference in average weight loss.[3][4]

Daily tablet or weekly injection: how are they taken?

Foundayo is taken as one tablet once a day. The UK leaflet states that it can be taken at any time of day, with or without food, and should be swallowed whole.[1]

The authorised Foundayo dose starts at 0.8mg once daily for 30 days. The dose is then increased to 2.5mg, with further increases possible after at least 30 days at each step. The maximum authorised daily dose is 17.2mg.[1]

Mounjaro is injected under the skin once a week. The UK SmPC states that it can be used at any time of day, with or without meals. The adult starting dose is 2.5mg once weekly, increasing to 5mg after four weeks; further 2.5mg increases can be made after at least four weeks on the current dose, up to a maximum of 15mg once weekly.[2]

Neither schedule is inherently more convenient for everyone. Foundayo avoids injections but needs to be taken every day. Mounjaro is injected, but only once a week. The practical preference depends on the individual rather than on the medicine format alone.

Why the dose numbers cannot be compared

A 17.2mg Foundayo tablet and a 15mg Mounjaro injection are not equivalent doses and cannot be ranked by the number of milligrams. They contain different active ingredients and reach the body in different ways.[1][2]

There is another detail worth knowing when reading the orforglipron research. ATTAIN-1 used an investigational capsule formulation, including a highest study dose of 36mg. Later phase 3 research explains that this 36mg capsule dose is equivalent to the 17.2mg tablet strength now authorised in the UK.[1][5] This is why an older trial paper may show a different milligram number from the current Foundayo pack.

Foundayo vs Mounjaro weight loss: what did the trials find?

This is the part of the comparison where precision matters most. Both medicines have strong placebo-controlled obesity trial evidence, but they were not tested against each other in the same randomised obesity efficacy study.[3][4]

Foundayo: ATTAIN-1

ATTAIN-1 randomised 3,127 adults with obesity and without diabetes to once-daily orforglipron or placebo for 72 weeks, alongside diet and physical-activity measures.[3]

At the highest study dose, average body-weight reduction at week 72 was 11.2% under the treatment-regimen estimand, compared with 2.1% with placebo. Under the efficacy estimand, which estimates the result if participants had remained on assigned treatment without prohibited additional weight-management treatment, the corresponding figures were 12.4% and 0.9%.[3]

Mounjaro: SURMOUNT-1

SURMOUNT-1 randomised 2,539 adults with obesity, or overweight with at least one qualifying weight-related condition, and without type 2 diabetes to weekly tirzepatide or placebo for 72 weeks.[2][4]

In the original trial analysis, mean body-weight reductions were approximately 15.0% with 5mg, 19.5% with 10mg and 20.9% with 15mg tirzepatide, compared with approximately 3.1% with placebo.[4]

The current UK Mounjaro SmPC also reports the efficacy-estimand results: 16.0% with 5mg, 21.4% with 10mg and 22.5% with 15mg, compared with 2.4% with placebo.[2]

Comparing the same type of analysis

The Mounjaro trial therefore reported substantially larger average reductions in body weight than the Foundayo trial at their highest studied doses.[2][3][4]

What these figures do not show is the exact difference that would occur if the same person took one medicine and then the other. Subtracting 11.2% from 20.9%, or describing one medicine as “twice as effective”, treats two independent trials as though they were a single head-to-head experiment. They were not.[3][4]

Is Foundayo as effective as Mounjaro?

The available evidence supports a more careful answer than either “yes” or “no”.Tirzepatide produced substantially greater mean weight reduction in SURMOUNT-1 than orforglipron produced in ATTAIN-1. That is a valid observation from the published data.[2][3][4]

However, those trials enrolled different groups of people and used separate protocols and analyses. They do not provide a randomised estimate of how much more or less weight the same patient would lose on Mounjaro compared with Foundayo. Nor do they establish that an individual will achieve the trial average on either medicine.[3][4]

For that reason, statements such as “Mounjaro is twice as effective as Foundayo” go beyond what the evidence proves.

Have Foundayo and Mounjaro been compared directly?

The obesity efficacy evidence currently available does not include a randomised trial that starts participants on orforglipron versus tirzepatide and compares weight loss between the two medicines from baseline. ATTAIN-1 compared orforglipron with placebo; SURMOUNT-1 compared tirzepatide with placebo.[3][4]

There is, however, a trial involving both medicines that answers a different question. ATTAIN-MAINTAIN studied what happened when people who had already lost weight on injectable tirzepatide or semaglutide moved to oral orforglipron or placebo.[5]

That makes it relevant to people asking about Foundayo after Mounjaro, but it is not a head-to-head test of which medicine causes more weight loss from the start.

What happened when people switched from tirzepatide to orforglipron?

In ATTAIN-MAINTAIN, participants had first completed 72 weeks of treatment in SURMOUNT-5. The tirzepatide cohort included 205 people, who were then randomised to once-daily orforglipron or placebo for a further 52 weeks.[5]

Among participants whose weight had plateaued before the switch, those assigned to orforglipron maintained an estimated 74.7% of the weight reduction previously achieved with tirzepatide, compared with 49.2% among those assigned to placebo.[5]

That is useful evidence, but the limitation is important. ATTAIN-MAINTAIN did not include a group that continued tirzepatide. The authors identify the lack of a continued-injectable comparator and the one-year trial duration as limitations.[5]

So the study supports this conclusion:

Orforglipron preserved more of the previous tirzepatide-associated weight reduction than placebo after a planned transition.[5]

It does not show that switching to Foundayo is equivalent to staying on Mounjaro, and it does not provide a consumer dose-conversion rule.

Do Foundayo and Mounjaro have the same side effects?

There is substantial overlap, particularly for gastrointestinal side effects, but their complete safety profiles are not identical.

The current UK Foundayo leaflet lists nausea, constipation, diarrhoea, vomiting, indigestion and abdominal pain as very common side effects. It also warns that nausea, vomiting and diarrhoea can cause dehydration.[1]

The UK Mounjaro SmPC likewise identifies gastrointestinal disorders as its most frequently reported adverse reactions. Nausea, diarrhoea, vomiting, constipation and abdominal pain are among the prominent effects, with nausea, diarrhoea and vomiting occurring particularly during dose escalation.[2]

It is not useful to turn separate trial percentages into a side-effect league table. Different studies include different participants and protocols, so a percentage from one trial is not a direct prediction of which medicine a particular person will tolerate better.

If nausea, vomiting or diarrhoea is persistent or makes it difficult to keep fluids down, seek medical advice. Both product documents warn about dehydration or fluid loss in connection with gastrointestinal side effects.[1][2]

Who can take Foundayo or Mounjaro for weight management?

For adult weight management in the UK, the authorised BMI criteria are broadly aligned. Both medicines are used alongside a reduced-calorie diet and increased physical activity for adults with either:

• a BMI of 30kg/m² or above; or
• a BMI from 27kg/m² to below 30kg/m² with at least one qualifying weight-related health condition.[1][2]

Foundayo and Mounjaro are prescription-only medicines. Meeting the basic licence criteria does not determine whether either treatment is appropriate for a particular person. Medical history, other medicines, previous response, side effects and individual risks all need to be considered by the prescriber.[1][2]

Is Foundayo better than Mounjaro?

Current evidence does not establish one medicine as the universally better option for every patient.

It does establish several concrete differences:

• Weight-loss trial results: the highest-dose tirzepatide group in SURMOUNT-1 had a substantially larger average weight reduction than the highest-dose orforglipron group in ATTAIN-1, but this was an indirect comparison between separate trials.[2][3][4]
• Treatment format: Foundayo is a daily tablet; Mounjaro is a weekly injection.[1][2]
• Mechanism: Foundayo activates the GLP-1 receptor; Mounjaro activates GIP and GLP-1 receptors.[1][2]
• Maintenance evidence: ATTAIN-MAINTAIN provides evidence for oral orforglipron after prior tirzepatide treatment, but does not compare that switch with continuing tirzepatide.[5]
• Clinical suitability: trial averages cannot settle which medicine is appropriate for an individual patient.[1][2]

That is the useful way to compare Foundayo with Mounjaro: separate what the trials observed from what they cannot tell you about an individual treatment decision.