What are the main differences between Foundayo and Mounjaro?
Foundayo (orforglipron) is a once-daily pill, whereas Mounjaro (tirzepatide) is a weekly injection. But the orforglipron vs tirzepatide difference goes beyond just format.
Foundayo is an oral GLP-1 receptor agonist. It copies a gut hormone that helps reduce appetite and slows how quickly food leaves your stomach. Mounjaro works on the same hormone but also acts on a second one called GIP, which enhances insulin release. That extra pathway is one reason Mounjaro produces greater weight loss.
The drawback is that Mounjaro is peptide-based. Your stomach would break it down before it could have a chance to work, so it can’t be given as a tablet. Mounajro is injected once a week instead.
These injections also need refrigerated storage. Foundayo is a non-peptide small molecule that survives digestion, so can be taken orally in the form of a daily pill. You can take it at any time of day, with or without food and water.
Mounjaro has been available in the UK since late 2023. The MHRA (Medicines and Healthcare products Regulatory Agency) licensed it for weight loss in UK markets. The National Institute for Health and Care Excellence (NICE) recommended it to be available through the NHS in December 2024.
Foundayo is a much newer weight loss treatment. Foundayo received FDA approval in April 2026. The FDA is the US medicines regulator, and for now the drug is only available there. No date has been set for an MHRA decision on UK approval, though it is expected in late-2026 or 2027.
Which produces more weight loss: Foundayo or Mounjaro?
Mounjaro produces roughly twice the weight loss of Foundayo at their highest doses. In the SURMOUNT-1 clinical trial, people taking Mounjaro at the highest dose (15 mg) lost an average 21% of their body weight over 72 weeks.Â
At the lowest treatment dose of 5 mg, average weight loss was around 15%. A placebo group received an inactive injection for comparison purposes. Average weight loss in that group was about 3%.
Foundayo’s results come from the ATTAIN-1 clinical trial, also over 72 weeks. At the highest dose, people lost an average of 11% of their body weight. The 12 mg dose came in at 8.4%, and the lowest tested dose was at about 7.5%. Placebo in that trial was about 2%.
Those figures include everyone enrolled, but not everyone stayed on treatment for the full 72 weeks. Accounting for people who dropped out early, Foundayo’s highest dose reached about 12% weight loss, compared with Mounjaro’s 22.5%. The gap remains large either way.
No one has tested Foundayo vs Mounjaro weight loss directly in the same trial. Both studies did enrol similar patients. All were adults who were obese, and none had type 2 diabetes.
That makes it reasonable to compare the results of the two separate trials. Wegovy (semaglutide) injections results sit between the two, producing about 15% average weight loss at the highest dose in the STEP-1 trial.
Foundayo produces less average weight loss than both Wegovy and Mounjaro. But people choosing Foundayo over injections are usually prioritising the flexibility of a daily pill. No needles, no fasting, and no rearranging your routine around a dosing schedule. Weight does tend to return after stopping either medication, so it is worth planning for the long term from the start.
Which has fewer side effects?
The side effects are similar in type and severity. Both Foundayo and Mounjaro can cause stomach-related side effects typical of all GLP-1 weight loss medications.
Nausea is the most commonly reported side effect for both. In the ATTAIN-1 trial, nausea affected roughly a third of people taking Foundayo at the highest dose. About 10% of people on placebo reported nausea. In SURMOUNT-1, nausea rates for Mounjaro were similar, ranging from around 24% to 33% depending on dose.
Constipation occurred in 20-27% of people on Foundayo compared to 12–17% on Mounjaro, depending on dose. Vomiting followed a similar pattern. Around 24% of people taking Foundayo at the highest dose reported vomiting, compared to 12% on Mounjaro depending on dose. Diarrhoea rates were broadly similar for both drugs, at roughly one in four people.
Most stomach-related side effects tended to happen when people first started treatment or when their dose was increased. These effects were usually short-lived and improved over time. Severe stomach-related side effects were uncommon in both trials.
The dosing schedule changes how side effects feel day-to-day. If nausea hits hard on Mounjaro, you cannot stop the medication from working through your system for the rest of the week. With Foundayo, pausing your daily dose for a day or two is more manageable.
Which is right for you?
Choosing between Foundayo and Mounjaro comes down to one question: is the extra weight loss worth more to you than the convenience of a daily pill? What feels right now, may not be the same for you in six months.
Mounjaro offers the strongest weight loss results currently available, and for some people, that matters more than convenience. Losing weight can help improve some weight-related health conditions. Often, the more weight that is lost, the more likely it is that these conditions may improve, but this varies from person to person.. Losing an extra 5–10% of your body weight can bring blood pressure down, improve blood sugar control, and take pressure off your joints.
Foundayo may be a better option for people who prefer an oral weight-loss treatment compared to an injectable one. Some people delay starting treatment because they are uncomfortable with needles. That is a more common barrier than most clinical comparisons acknowledge.
A weekly injectable GLP‑1 that needs to be stored in the fridge can be enough to put some people off starting treatment. Others travel frequently and find a weekly injection routine difficult to maintain. Foundayo helps remove both barriers by offering a daily oral option.
Availability reduces the choice for UK patients right now. Mounjaro is licensed here and available through the NHS (in eligible cases) or privately. The MHRA has not yet approved Foundayo, and you can only get it in the US.
If you are looking to start treatment now, Mounjaro and Wegovy (semaglutide) injections are the options currently available. If you are looking for an oral weight-loss treatment option that is available in the UK, the Wegovy Pill may be an option for you.
We prescribe both Mounjaro and injectable Wegovy for weight management. No one knows yet whether people stick with a daily pill longer than a weekly injection. But removing barriers to starting treatment counts for something.
When should I see a doctor?
Most side effects are mild and can be managed with the help of our clinical team, but some symptoms need urgent attention.
For both medications, contact our clinical team if you experience:
- Mild nausea or vomiting that is not stopping you from keeping fluids down
- Diarrhoea or constipation that has carried on beyond the first few weeks
- Reflux, bloating, or appetite changes that are getting in the way of your daily routine
- Any uncertainty about your dose, whether that means stepping up, staying put, or taking a break
For serious symptoms, more prompt action is needed:
| Symptoms | What it may indicate | What to do |
| A lump or swelling in your neck, hoarseness, or difficulty swallowing | Thyroid problems | See your GP or call NHS 111 |
| Yellowing of the skin or eyes, or severe pain in the upper right side of your abdomen | Gallbladder problems | See your GP or call NHS 111 |
| Vomiting for more than 6 hours and struggling to keep fluids down | Dehydration risk | See your GP or call NHS 111 |
| Shaking, sweating, confusion, or dizziness | Low blood sugar | See your GP or call NHS 111 |
| Severe abdominal pain that spreads to your back and does not ease, with or without vomiting | Pancreatitis | Stop your medication. Call 999 or go to A&E |
| Swelling of the face, lips, tongue, or throat, difficulty breathing, or widespread rash | Severe allergic reaction | Stop your medication. Call 999 or go to A&E |
| Unusually dark urine, dizziness on standing, or confusion after repeated vomiting or diarrhoea | Severe dehydration | Stop your medication. Call 999 or go to A&E |
| Sudden changes in vision, including loss of vision in one eye | A rare eye condition called NAION | Stop your medication. Call 999 or go to A&E |
| Thoughts of self-harm or suicide | Mental health crisis | Go to A&E and ask for the CRISIS team |
Key takeaways
- In clinical trials people taking Mounjaro at the highest dose lost 21% of their body weight over 72 weeks. Foundayo’s highest dose produced 11%. That is roughly a twofold difference.
- The two medications work differently. Mounjaro is a weekly injection targeting both GLP-1 and GIP receptors. Foundayo is a daily pill that targets GLP-1 receptors alone.
- Both medications cause similar side effects. Nausea, diarrhoea, constipation, and vomiting are the most common, and they usually settle within the first few weeks.
- You can take Foundayo at any time of day with no food or water restrictions. If you do not want injections, Foundayo may be a good choice. If you do not want a strict dosing schedule, it may also work well. Right now, Foundayo is the most flexible oral GLP-1 option available.
- Mounjaro is available in the UK now. Foundayo does not yet have MHRA approval and is only available in the United States.
References
Orforglipron, an Oral Small-Molecule GLP-1 Receptor Agonist for Obesity Treatment (ATTAIN-1), New England Journal of Medicine, 2025 [Accessed 26 May 2026].
Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1), New England Journal of Medicine, 2022 [Accessed 26 May 2026].
Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1), New England Journal of Medicine, 2021 [Accessed 26 May 2026].
Weight Regain After Cessation of Medication for Weight Management: Systematic Review and Meta-Analysis, The BMJ, 2026 [Accessed 26 May 2026].
Foundayo (orforglipron) Prescribing Information, U.S. Food and Drug Administration, 2026 [Accessed 26 May 2026].
Mounjaro (tirzepatide) Summary of Product Characteristics, Electronic Medicines Compendium (emc), 2024 [Accessed 26 May 2026].
Tirzepatide for managing overweight and obesity (TA1026), National Institute for Health and Care Excellence (NICE), 2024 [Accessed 26 May 2026].
Authorship
Authored by Shereen Amin
Pharmacist Independent Prescriber & Medical Writer
GPhC: 2073003
Shereen is a Pharmacist Independent Prescriber and medical writer with over ten years' experience across NHS primary care, digital health and specialist services. She writes evidence-based health content for Simple Online Pharmacy, turning complex clinical information into guidance patients can actually use.
Medically Reviewed by Zahra Qureshi
Senior Pharmacist
GPhC: 2216331
Zahra began her pharmacy career in community pharmacy, building a strong foundation in patient care and medication safety. She joined Simple Online Pharmacy as a locum pharmacist and quickly progressed to a senior role, supporting the pharmacy and operations teams. Zahra is passionate about ensuring patient guidance is safe, clinically sound, and easy to understand, making a positive difference to patients’ lives.
