Switching From Mounjaro to Foundayo

As Foundayo tablets become available in the UK, many patients currently using Mounjaro injections are asking whether they can switch from a once-weekly tirzepatide injection to a once-daily orforglipron tablet.

However, Mounjaro and Foundayo contain different active ingredients and there is no manufacturer-approved dose-for-dose conversion guide between the two medicines.

This means that switching should always take place following an indiviual clinical assessment.

At Pharmulous, our prescribing clinicians consider your current Mounjaro dose, treatment history, tolerability, weight-management progress and the time since your last injection before recommending an appropriate Foundayo starting dose.

Can You Switch From Mounjaro to Foundayo?

Some patients who are already established on Mounjaro may be suitable for switching to Foundayo tablets following clinical review.

There are several reasons why someone may consider moving from an injection to a tablet, including:

• Preference for a tablet rather than an injection
• Needle anxiety
• A preference for a daily treatment routine
• Easier storage and travel
• Long-term treatment planning
• Looking for an alternative option during weight maintenance
• Cost considerations

However, Foundayo is not simply Mounjaro in tablet form.

The two medicines work differently and their doses are not directly interchangeable.

Treatment decisions should take into account:

• Your current Mounjaro dose
• How long you have been taking that dose
• When you took your last injection
• Any gaps in treatment
• Your response to Mounjaro
• Side effects and tolerability
• Your current weight and weight-management goals
• Your medical history
• Other medicines you take

Mounjaro vs Foundayo: What's the Difference?

Mounjaro contains tirzepatide and is administered as a once-weekly injection.

Tirzepatide acts on both GIP and GLP-1 receptors.

Foundayo contains orforglipron, an oral GLP-1 receptor agonist taken once daily.

Foundayo acts on the GLP-1 receptor and can help reduce appetite and food intake as part of a wider weight-management programme.

Both medicines are prescription-only treatments and should be used alongside appropriate dietary and lifestyle measures.

Although they share some similarities, switching between the two is not a direct equivalent-dose change.

Pharmulous Mounjaro to Foundayo Switching Guide

The table below outlines the switching approach currently used by Pharmulous clinicians for selected patients who are established and tolerating Mounjaro treatment.

Important information about this switching guide

This table is a Pharmulous clinical switching guide and not a manufacturer-approved dose-equivalence chart.

The standard licensed Foundayo initiation schedule begins at 0.8 mg once daily, followed by 2.5 mg, 5.5 mg, 9 mg, 14.5 mg and 17.2 mg, with at least 30 days between dose increases where appropriate.

Starting Foundayo at a dose above 0.8 mg therefore differs from the standard licensed initiation schedule and requires an individual prescribing decision.

The purpose of the switching guide is to take into consideration a patient's existing exposure and established tolerability to incretin-based treatment rather than treating every established Mounjaro patient as if they were completely new to treatment.

What Evidence Is There for Switching?

An important study called ATTAIN-MAINTAIN, published in Nature Medicine in 2026, investigated switching patients from injectable weight-management treatment to oral orforglipron.

Participants had previously completed 72 weeks of treatment with either:

• tirzepatide 10 mg or 15 mg, or
• semaglutide 1.7 mg or 2.4 mg.

Rather than starting orforglipron at its lowest study dose, patients transitioning to oral treatment started directly at 12 mg of the investigational orforglipron capsule.

This is important because the Foundayo product information confirms that the 12 mg study capsule provides equivalent exposure to the licensed Foundayo 9 mg tablet.

The trial therefore provides direct clinical evidence that selected patients already established and tolerant on tirzepatide 10 mg or 15 mg were able to transition to the equivalent of Foundayo 9 mg daily.

However, the study did not directly investigate every Mounjaro dose.

The lower-dose recommendations within the Pharmulous table are therefore based on clinical extrapolation and prescribing judgement rather than direct dose-equivalence studies.

How Long Can the Gap Be Between Mounjaro and Foundayo?

This is an important part of the Pharmulous switching pathway.

The above switching guide is intended for patients who are currently established on Mounjaro and have not had a treatment gap of more than 14 days since their last injection.

In the ATTAIN-MAINTAIN study, the first dose of orforglipron was intended to be administered within 14 days of the patient's final injectable treatment.

For this reason, Pharmulous would not routinely use the higher-dose switching pathway where the gap since the patient's last Mounjaro injection exceeds 14 days.

In practical terms:

Up to 14 days since your last Mounjaro injection:

The Pharmulous switching guide may be considered, subject to clinical assessment and good tolerability of your previous treatment.

More than 14 days since your last Mounjaro injection:

The switching table should not automatically be applied. Your treatment history will need to be reviewed by a prescribing clinician and a lower Foundayo starting dose may be recommended.

If the date of your last dose cannot be confirmed:

A clinician may recommend starting at a lower dose rather than using the accelerated switching pathway.

This approach helps reduce the risk of restarting at a dose that may no longer be well tolerated following a break from treatment.

When Should I Take My First Foundayo Tablet?

For patients switching directly from Mounjaro, Foundayo would commonly be started at around the time the next weekly Mounjaro injection would normally have been due.

For example:

If you take your final Mounjaro injection on a Monday, you may be advised to start Foundayo approximately the following Monday.

This approximately seven-day interval is a practical switching approach based around Mounjaro's weekly dosing schedule.

It is important to note that the ATTAIN-MAINTAIN study itself did not establish seven days as a specific required washout period. Instead, participants started orforglipron within 14 days of their previous injectable treatment.

The exact timing of your first Foundayo dose should therefore be confirmed by your prescribing clinician.

Do I Need to Start Foundayo at 0.8 mg?

Not necessarily if you are already established on another incretin treatment, but this requires clinical assessment.

For someone starting Foundayo without recent incretin treatment, the licensed starting dose is 0.8 mg once daily.

However, patients who have already demonstrated good tolerance to Mounjaro may be considered differently.

ATTAIN-MAINTAIN provides evidence that selected patients established on high-dose tirzepatide could start oral orforglipron at a higher dose without first progressing through every lower dose.

This does not mean that every patient switching from Mounjaro should start at a higher Foundayo dose.

Your prescriber will consider:

• Your current Mounjaro dose
• How long you have been established on treatment
• Whether you have tolerated it well
• Any current nausea, vomiting, diarrhoea or constipation
• Your treatment gap
• Current weight and weight trajectory
• Your medical history and other medication

If there are concerns about tolerability or a significant interruption in treatment, starting at a lower Foundayo dose may be more appropriate.

What Should I Expect After Switching?

Although both medicines influence appetite, they are different medicines and you may notice some changes after switching.

These could include temporary differences in:

• Appetite suppression
• Hunger levels
• Food cravings
• Feelings of fullness
• Gastrointestinal side effects
• Weight-loss rate
• Weight stability during maintenance

This does not necessarily mean the new treatment is not working.

It can take time for your body to adjust to a different medicine and dosing schedule.

Regular review is therefore useful after switching, particularly during the first few weeks.

Can Foundayo Help With Weight Maintenance After Mounjaro?

This is one of the particularly interesting areas of research around orforglipron.

ATTAIN-MAINTAIN specifically investigated patients who had already achieved substantial weight loss with injectable tirzepatide or semaglutide.

Patients who moved to orforglipron maintained significantly more of their previous weight reduction over the following 52 weeks than those who switched to placebo.

Among participants who had reached a weight plateau:

Patients previously treated with tirzepatide maintained approximately 75% of their previous weight reduction when switched to orforglipron, compared with approximately 49% with placebo.
Patients previously treated with semaglutide maintained approximately 79%, compared with approximately 38% with placebo.
This provides encouraging evidence for oral orforglipron as a potential longer-term treatment option following successful weight loss with injectable therapy.

However, individual results vary and treatment should always be tailored to the individual.

What Are the Common Side Effects of Foundayo?

Like other GLP-1 receptor agonists, Foundayo can cause gastrointestinal side effects.

These may include:

• Nausea
• Vomiting
• Diarrhoea
• Constipation
• Indigestion
• Abdominal discomfort

People who are already well established on incretin-based treatment may have developed some tolerance to gastrointestinal effects, but this cannot be assumed for every patient.

Any persistent, severe or concerning symptoms should be discussed with a healthcare professional.

Our Clinical Approach at Pharmulous

At Pharmulous, we do not believe that switching treatment should simply mean matching one number to another.

Our clinicians assess each patient individually.

When considering a switch from Mounjaro to Foundayo, we look at:

• Current treatment and dose
• Evidence of recent treatment
• Date of the last Mounjaro injection
• Duration on the current dose
• Previous side effects
• Current weight and weight-management progress
• Treatment goals
• Maintenance requirements
• Individual tolerability

Our approach continues to focus on finding the lowest effective and well-tolerated dose that supports the patient's individual weight-management goals.

If you are considering switching treatment, or wondering whether your current treatment is still the right fit for you, send us a message through the patient portal.

One of our prescribing clinicians will be happy to talk you through the available options and help you decide on the most appropriate next step for your individual needs.

Key Takeaways

• Some established Mounjaro patients may be suitable for switching to Foundayo tablets.
• Mounjaro and Foundayo are different medicines and there is no direct mg-for-mg conversion.
• Pharmulous uses a clinician-led switching guide based on previous treatment exposure and tolerability.
• The licensed Foundayo starting dose is 0.8 mg once daily.
• Starting above 0.8 mg requires an individual prescribing decision.
• ATTAIN-MAINTAIN provides direct switching evidence for patients previously established on tirzepatide 10 mg or 15 mg.
• The Pharmulous higher-dose switching pathway should generally only be considered where the patient's last Mounjaro dose was within the previous 14 days.
• Patients with a gap of more than 14 days require individual review and may need to restart Foundayo at a lower dose.
• The exact timing and dose of any switch should always be confirmed by a qualified prescribing clinician.
  Ongoing monitoring remains important after changing treatment.

Useful Links

Pharmulous Weight Loss
Pharmulous Weight Maintenance
Foundayo information
Mounjaro information

References

1. Aronne LJ, Horn DB, le Roux CW, et al. Orforglipron for maintenance of body weight reduction: the double-blind, randomized phase 3b ATTAIN-MAINTAIN trial. Nature Medicine. 2026;32:2679–2687.
2. Eli Lilly and Company Limited. Foundayo (orforglipron) Summary of Product Characteristics. Electronic Medicines Compendium. 2026.
3. Eli Lilly and Company Limited. Mounjaro (tirzepatide) Summary of Product Characteristics. Electronic Medicines Compendium.
4. Medicines and Healthcare products Regulatory Agency (MHRA). GLP-1 medicines for weight loss and diabetes: information for patients and healthcare professionals.