Foundayo side effects by dose
Trials used 6 mg, 12 mg, and 36 mg capsules, while UK prescriptions use 5.5 mg, 9 mg, and 17.2 mg tablets.
Because the formulations are absorbed differently, the UK product information lists three tablet and capsule dose pairs as equivalent. These are 5.5 mg and 6 mg, 9 mg and 12 mg, and 17.2 mg and 36 mg.1
Foundayo starts at 0.8 mg, then increases to 2.5 mg so a prescriber can see how well it’s tolerated.1
| Side effect |
Placebo |
Foundayo 5.5 mg |
Foundayo 9 mg |
Foundayo 17.2 mg |
| Nausea |
10% |
26% |
34% |
35% |
| Constipation |
9% |
20% |
27% |
24% |
| Diarrhoea |
11% |
21% |
23% |
25% |
| Vomiting |
4% |
13% |
21% |
24% |
| Indigestion |
4% |
12% |
16% |
13% |
| Abdominal pain |
7% |
13% |
14% |
14% |
| Headache |
7% |
8% |
9% |
9% |
| Bloating |
3% |
7% |
9% |
8% |
| Tiredness (fatigue) |
4% |
6% |
7% |
9% |
| Burping |
1% |
6% |
8% |
8% |
| Reflux or heartburn |
2% |
6% |
6% |
7% |
| Wind |
2% |
5% |
6% |
6% |
| Hair loss |
2% |
4% |
4% |
5% |
These figures come from the pooled ATTAIN-1 and ATTAIN-2 trials, which included 3,155 participants living with overweight or obesity who took Foundayo and 1,576 who took a placebo.2,3
Dizziness, a faster heartbeat, low blood pressure, and gallstones are also listed as common side effects in the UK product information.1
Constipation, indigestion, and bloating were slightly more common at 9 mg than 17.2 mg, so individual symptoms don’t always become more common at higher doses.
Side effects are most likely during dose increases
Foundayo slows the rate at which our stomach empties after eating. This can contribute to nausea, vomiting, indigestion, bloating, and abdominal pain.1
Nausea, vomiting, and diarrhoea were most common during dose increases and became less common over time.
Across the Foundayo clinical trials, 61.8% of digestive side effects were mild, 34.3% moderate, and 3.9% severe.1
Each Foundayo dose is taken for at least 30 days. The UK product information says to increase the dose only if the medicine is working (leading to weight loss) and the current side effects are manageable.1
Mild nausea and temporary bowel changes often ease as treatment continues. Speak to your prescriber before the next dose increase if symptoms persist, affect eating, drinking, or daily life, or worsen.
The dose may need to stay the same for longer or be reduced. Don’t change it without discussing the symptoms with your prescriber.
Managing nausea, vomiting, constipation, and diarrhoea
Foundayo slows stomach emptying, so large meals can worsen nausea, reflux, bloating, and vomiting. Eating a diet based mainly on whole foods, eating more slowly, and reducing portion sizes may help to manage these symptoms (eating more whole foods can inherently reduce the calorie content of our meals).
Sip fluids regularly, avoid lying down after eating, and make a note which specific foods seem to trigger your symptoms so you can avoid them in the future.6
If you’re feeling nauseated, try plain foods without a strong smell, but we still recommend eating 3 balanced meals a day to ensure you’re providing your body with the nutrients it needs.
If you’re really struggling to eat due to nausea, try foods that are easier to digest, like smoothies, or soups with a source of protein on the side.
If you’re constipated, drink plenty of fluids and gradually add more fibre from vegetables, fruit, beans, lentils, nuts, seeds, and wholegrains. Regular movement and placing your feet on a small footstool while using the toilet may also help.
Don’t keep adding fibre if constipation comes with severe pain, marked swelling, vomiting, or an inability to pass stool or wind.
Vomiting or diarrhoea can cause dehydration. Contact a healthcare professional if you’re vomiting more than three times a day, can’t keep fluids down, have dark urine, or feel light-headed.6
Nausea, heartburn, and vomiting often improve within three to four weeks of starting a weight-loss medication or increasing the dose.6
Our guide to the first month on Foundayo discusses the starting dose, appetite changes, and early weight-loss expectations.
Foundayo and hair loss
Hair loss affected 4% to 5% of people taking Foundayo in the clinical Foundayo trials, compared with 2% taking a placebo.2
The difference was larger among women, with 7% reporting hair loss on Foundayo and 3% on placebo. Among men, the rates were 0.9% and 0.7%.2
Rapid weight loss and undereating are the most likely causes of hair loss on Foundayo. In clinical trials, most cases were temporary and occurred while participants were losing weight, suggesting the medication isn’t directly damaging hair follicles.1
To reduce the risk of hair loss, avoid losing weight too quickly and make sure you’re eating enough calories and protein.
We recommend eating a diet based on whole foods that contains enough protein, fibre, fat, and complex carbohydrates.
Include iron-rich foods such as red meat, beans, lentils, nuts, seeds, and leafy green vegetables with a source of vitamin C (kale alongside tomatoes, for example, as the vitamin C increases iron absorption).
Speak to your GP if the hair loss is patchy, your scalp is sore or inflamed, or you also feel unusually tired, cold, or dizzy, as these symptoms may point to another cause.
How Foundayo’s side effects compare with the Wegovy pill
In separate clinical trials, nausea and vomiting were reported more often with the Wegovy pill. Constipation and diarrhoea were reported more often with Foundayo, while more people stopped Foundayo because of side effects.3,8
ATTAIN-1 included 728 people who received the highest orforglipron dose. OASIS 4 included 204 people who received the 25 mg Wegovy pill.
Both trials included adults living with overweight or obesity without type 2 diabetes. Because the medicines were tested in separate trials, differences in participants, dosing schedules, and how side effects were recorded may have affected the reported side effects.3,8
| Comparison |
Foundayo 17.2 mg* |
Wegovy pill 25 mg |
| People included in the side-effect analysis |
728 |
204 |
| Nausea |
33.7% |
46.6% |
| Vomiting |
24.0% |
30.9% |
| Constipation |
25.4% |
20.1% |
| Diarrhoea |
23.1% |
17.6% |
| Stopped because of digestive side effects |
7.0% |
3.4% |
| Stopped because of any side effect |
10.3% |
6.9% |
| Average weight loss |
11.2% at 72 weeks |
13.6% at 64 weeks |
| How it’s taken |
Once a day at any time, without food or water restrictions |
Once a day after at least 8 hours without food, followed by a 30-minute wait before eating, drinking, or taking another oral medicine |
*ATTAIN-1 tested a 36 mg orforglipron capsule. The UK product information states that this produces the same clinical effect as the approved 17.2 mg Foundayo tablet because the formulations are absorbed differently.1
Nausea affected 46.6% of people taking the Wegovy pill and 33.7% taking Foundayo. Vomiting affected 30.9% and 24.0%, respectively.
Constipation affected 25.4% of people taking Foundayo and 20.1% taking the Wegovy pill. Diarrhoea rates were 23.1% and 17.6%.
7% of people taking Foundayo stopped because of digestive side effects, compared with 3.4% taking the Wegovy pill. When all side effects were included, 10.3% stopped taking Foundayo, and 6.9% stopped the Wegovy pill.3,8
The separate trials can’t tell us why more people stopped taking Foundayo. The difference could be due to dose schedules, participants, or how each trial recorded side effects.
However, the discontinuation figures suggest that Foundayo may be harder to tolerate overall, despite causing less nausea and vomiting.
ACHIEVE-3 compared orforglipron and oral semaglutide under the same trial conditions. Digestive side effects affected 58% to 59% of people taking orforglipron and 37% to 45% taking oral semaglutide.
Between 8.7% and 9.7% stopped taking orforglipron because of side effects, compared with 4.5% to 4.9% taking oral semaglutide.4
ACHIEVE-3 used the 7 mg and 14 mg oral semaglutide doses for type 2 diabetes rather than the 25 mg Wegovy pill. It doesn’t directly address the Wegovy pill comparison, but more people stopped taking orforglipron when both medicines were tested in the same trial.
Average weight loss was 11.2% with the highest Foundayo dose over 72 weeks and 13.6% with the Wegovy pill over 64 weeks. These figures include everyone who entered the trials, whether or not they completed treatment.3,8
Foundayo can be taken once a day at any time, without restrictions around food or water.
The Wegovy pill must be taken after at least 8 hours without food, with no more than 120 mL of water. You then need to wait 30 minutes before eating, drinking, or taking another oral medicine.1,9
Based on the evidence available, the Wegovy pill produced more weight loss, and fewer people stopped taking it because of side effects. Foundayo has a simpler dosing routine, but more people stopped taking it.
Serious side effects and when to get help
Acute pancreatitis may affect up to 1 in 100 people. The frequency of bowel obstruction, severe allergic reactions, dehydration-related kidney problems, and sudden vision changes is unknown.1
Gallstones affected 1.3% of people taking Foundayo and 0.6% taking a placebo in the clinical trials, most likely due to losing weight too quickly. Gallstones can cause gallbladder inflammation or block a bile duct.1
Each of the symptoms below needs urgent assessment:
- Severe, persistent abdominal pain, particularly if it spreads to the back, may be acute pancreatitis (inflammation of the pancreas). Seek urgent medical help, especially if it comes with vomiting.
- Persistent pain under the right ribs, fever, or yellow skin or eyes can indicate gallbladder inflammation or a blocked bile duct. Contact NHS 111 or seek urgent care.
- Severe abdominal pain, marked swelling, vomiting, or being unable to pass stool or wind can indicate a bowel obstruction. Seek urgent medical assessment.
- Swelling of the face, lips, tongue, or throat, trouble breathing, or collapse can indicate a serious allergic reaction. Call 999.
- Sudden loss of vision or rapidly worsening sight needs urgent assessment. Rapid improvements in blood sugar can also temporarily worsen diabetic eye disease.
Repeated vomiting or diarrhoea can reduce blood flow to the kidneys through dehydration. The risk is greater for people with kidney problems or those taking medicines that affect fluid balance.1,2
Foundayo can also lower blood sugar when combined with insulin (the hormone that manages blood sugar) or a sulfonylurea diabetes medicine.
Sweating, shaking, hunger, confusion, or a fast heartbeat can be signs of hypoglycaemia (blood sugar below a healthy level), and any diabetes medications you’re on may need adjusting.1
Tell the clinical team that you take Foundayo before an operation or procedure involving deep sedation. Slower stomach emptying can leave food in the stomach and increase the risk of it entering the lungs during anaesthesia.1
The UK and U.S. thyroid-cancer warnings are different
The UK Foundayo information doesn’t list thyroid cancer, medullary thyroid carcinoma, or multiple endocrine neoplasia type 2 as contraindications (reasons not to prescribe a medicine). Its only listed contraindication is an allergy to orforglipron or another tablet ingredient.1
The U.S. prescribing information has a boxed warning about thyroid C-cell tumours. It says people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 shouldn’t take Foundayo.2
Other GLP-1 medications caused thyroid C-cell tumours in rodent studies. Foundayo doesn’t activate the GLP-1 receptor in standard rat or mouse models and didn’t cause tumours in its rodent studies.1,2
The UK product information says rodent findings with GLP-1 medicines are unlikely to predict the risk in humans, although a human risk can’t be completely excluded.1
Human research hasn’t established an increased thyroid-cancer risk. A Scandinavian study compared 145,410 people who started a GLP-1 medication with 291,667 who started another diabetes medicine and followed the GLP-1 group for an average of 3.9 years.5
The rates were 1.33 cases with GLP-1 treatment and 1.46 with the comparison medicines for every 10,000 people followed for a year. The study found no increased risk, although it couldn’t exclude a very rare effect or one that develops after longer use.5
The UK product information doesn’t state why its warning differs from the U.S. label. Its position is consistent with Foundayo’s negative rodent studies and human research that hasn’t found an increased risk.
The evidence still can’t rule out a very rare risk or one that takes longer to develop.
If you have a personal or family history of thyroid cancer or a related inherited condition, tell your prescriber so they can assess your individual history. People taking Foundayo in the U.S. should follow the U.S. prescribing information.
Foundayo and the contraceptive pill
Foundayo may make oral hormonal contraception less reliable for a short period. Use a barrier method such as condoms, or change to a non-oral method, for 30 days after starting Foundayo and for 30 days after every dose increase.1
Don’t use Foundayo during pregnancy or breastfeeding. If you’re planning a pregnancy, speak to your prescriber and stop Foundayo at least three weeks beforehand.1
Some antibiotics, antifungal medicines, epilepsy treatments, cholesterol medicines, ciclosporin, and St John’s wort can change the amount of Foundayo or another medicine in the blood.
Give your prescriber and pharmacist a complete list of medicines, supplements, and herbal remedies you’re taking before starting Foundayo.1
Frequently asked questions
How long do Foundayo side effects last?
Nausea, heartburn, and vomiting often improve within three to four weeks of starting or increasing a GLP-1 medication, but Foundayo trials haven’t established how long each symptom lasts.
Constipation may last longer, and you should review persistent symptoms before the next dose increase.1,6
What side effects should I expect on Foundayo 0.8 mg?
The 0.8 mg starting dose can still cause nausea, constipation, diarrhoea, vomiting, indigestion, or abdominal pain.
The main trials didn’t publish a separate percentage for 0.8 mg, so rates from the 5.5 mg dose shouldn’t be presented as starting-dose rates.
What time of day should I take Foundayo?
You can take Foundayo at any time of day, with or without food and water. Taking it at a consistent time may make it easier to remember, but there’s no trial evidence that morning or evening dosing prevents nausea.1
What foods should I avoid while taking Foundayo?
We recommend basing your diet mainly on whole foods while taking Foundayo. It may help to reduce the frequency and severity of side effects, improve weight-loss outcomes, and will lead to more health benefits than eating a diet based more on ultra-processed foods.
Can you drink alcohol with Foundayo?
The UK product information doesn’t list a direct interaction with alcohol. Alcohol can worsen nausea, reflux, dehydration, and low blood sugar, particularly for people taking insulin or a sulfonylurea, so ask your prescriber what a safe amount for you is.1,6
Broadly, we’d recommend limiting alcohol intake for overall health benefits, not just because it could worsen side effects while you’re on Foundayo.
Can you take Foundayo and Mounjaro together?
No. Don’t take Foundayo and Mounjaro together.
Both medicines activate the GLP-1 receptor, and the combination hasn’t been tested. Taking them together could increase side effects without evidence that it improves weight loss.2
If you’re switching between them, follow your prescriber’s schedule. Don’t take your first Foundayo tablet until your prescriber tells you to.
Does Foundayo build up in your system?
Yes. Foundayo has a half-life of 29 to 49 hours, which means the body takes roughly one to two days to remove half of each dose.
Because Foundayo is taken every day, some of the previous dose remains in the body when the next tablet is taken. The amount rises over the first week and then stabilises, as long as the dose stays the same.1
Can I safely stop taking Foundayo?
Foundayo isn’t known to cause withdrawal symptoms, but hunger and food noise can return after it’s stopped.
Speak to your prescriber before stopping, particularly if you take it for type 2 diabetes or are stopping because of side effects.
Is Foundayo safe?
The MHRA approved Foundayo because its benefits outweigh its known risks for eligible people who are monitored appropriately.
The medicine is under additional monitoring because it’s new, which helps regulators identify uncommon effects as use increases.1
Take home message
Foundayo’s most common side effects are nausea, constipation, diarrhoea, vomiting, indigestion, and abdominal pain. Dizziness, headache, tiredness, gallstones, and hair loss are also common.
Still, some of the side effects, like hair loss, are more closely linked to side effects relating to losing weight too quickly, rather than being directly caused by the drug.
Digestive side effects affected 60% to 69% of people taking Foundayo in the clinical trials. Most were mild or moderate, and symptoms were more likely as the dose increased.
At Second Nature, we recommend staying on the lowest effective dose for as long as possible. If you’re losing weight sustainably and managing side effects, there’s no clinical reason to switch.
In ACHIEVE-3, 8.7% to 9.7% stopped taking orforglipron because side effects impaired quality of life, compared with 4.5% to 4.9% taking oral semaglutide.
Severe persistent abdominal pain, signs of bowel obstruction, a serious allergic reaction, or a sudden vision change need urgent assessment.
People using the contraceptive pill need additional or non-oral contraception for 30 days after starting and after every dose increase.
Second Nature combines GLP-1 medication with registered dietitian support and structured habit change. Building habits around food, movement, and emotional eating while taking the medication can also reduce the risk of weight regain if you come off the medication in the future.
In a published service evaluation, active Second Nature members lost an average of 19.1% of their starting weight at 12 months, and 77.7% lost at least 10%.7
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
