Oral GLP-1 Side Effects: What to Expect from Tablet Treatment

GLP-1 tablets, including Wegovy tablets (oral semaglutide) and Foundayo (orforglipron), cause much the same side effects as weekly GLP-1 injections, because they act on the same receptors. The most common are nausea, vomiting, diarrhoea, constipation and indigestion. In the main trials these were usually mild to moderate and most frequent while the dose was being increased, but they were also the most common reason people stopped. Serious problems such as pancreatitis and gallbladder disease are uncommon but important to recognise. This guide explains what to expect, how often each side effect occurred in trials, and when to get help.

The GLP-1 tablets available in the UK

At the time of writing, there are three GLP-1 tablets on the UK market, with different licences:

• Wegovy tablets (oral semaglutide): authorised by the MHRA in June 2026 for weight management in adults with obesity, or overweight with at least one weight-related condition. The dose rises from 1.5mg daily through 4mg and 9mg to 25mg.
• Foundayo (orforglipron): authorised by the MHRA in August 2026 for weight management and for type 2 diabetes. It is a small-molecule medicine, not a peptide, and can be taken without food or water restrictions.
• Rybelsus (oral semaglutide): licensed for type 2 diabetes only, at lower doses. See Rybelsus and weight loss.

Regulatory details can change, so check the MHRA and the current Summary of Product Characteristics (SmPC) for your medicine. For background on each, see our oral semaglutide guide and Foundayo guide.

Why GLP-1 tablets cause side effects

GLP-1 medicines slow the rate at which the stomach empties and act on areas of the brain involved in appetite and nausea. These are the same effects that reduce hunger and help people eat less. When food stays in the stomach longer, it can cause fullness, bloating, burping, reflux and nausea, particularly after large or fatty meals. Changes in gut movement further down can cause diarrhoea or constipation.

The body usually adapts over time, which is why doses start low and rise in steps, normally at least four weeks apart. Side effects often return briefly after each increase.

The route of delivery does not change these effects. A tablet delivers the medicine into the bloodstream by a different path, but once there it acts on the same receptors as an injection.

How common are side effects? What the trials found

The figures below come from published trials. They are averages across groups and give an idea of likelihood, not a prediction for any individual.

Oral semaglutide

OASIS 4 (New England Journal of Medicine, 2025) compared oral semaglutide 25mg daily with placebo for 64 weeks in around 300 adults with overweight or obesity who did not have diabetes.

Most gastrointestinal events were mild to moderate and temporary. The serious adverse event rate was not higher with oral semaglutide in this trial, though the trial was too small to detect rare problems reliably.

OASIS 1 (The Lancet, 2023) tested a higher 50mg daily dose for 68 weeks. Gastrointestinal side effects were reported by around four in five people on oral semaglutide, compared with under half on placebo. The 50mg dose is not the one licensed in the UK.

Orforglipron

ATTAIN-1 (New England Journal of Medicine, 2025) compared three doses of orforglipron with placebo for 72 weeks in over 3,000 adults with obesity, or overweight with a weight-related condition, without diabetes. The most common side effects were nausea, constipation, diarrhoea, vomiting and indigestion. Most were mild to moderate and occurred during dose escalation. The proportion of people who stopped treatment because of side effects was higher with orforglipron than with placebo and rose with the dose, reaching around one in ten at the highest dose in published results.

How this compares with injections

For context, in STEP 1 (semaglutide 2.4mg weekly injection, NEJM 2021), around three-quarters of participants reported gastrointestinal side effects, compared with under half on placebo. These rates are broadly in the same range as the tablet trials. Cross-trial comparisons are imprecise because of differences in trial design, so they cannot show that one form is better tolerated than another. Our comparison of oral and injectable GLP-1s looks at this in more detail.

Common side effects and how they are managed

Nausea

Nausea is the most frequently reported side effect. It is often worst in the hours after eating, especially after large or rich meals. Practical steps that many people find helpful include:

• Eating smaller meals, slowly, and stopping as soon as you feel full
• Avoiding very fatty, fried or spicy foods, particularly early in treatment
• Not lying down straight after eating
• Sipping cold water or other fluids through the day
• Eating bland foods, such as toast or crackers, when nausea is bad

If nausea is persistent, your prescriber may suggest staying at the current dose for longer before stepping up. See our full guide to managing nausea on GLP-1 medication and foods that can worsen GLP-1 side effects.

Vomiting

Vomiting was reported often in the oral semaglutide trials. Occasional vomiting may settle, but repeated vomiting can lead to dehydration, which in turn can strain the kidneys. If you cannot keep fluids down, seek advice promptly.

There is also a practical point for oral semaglutide. If you vomit soon after taking your tablet, do not take another one; follow the advice in the patient leaflet and resume the next day as normal.

Diarrhoea

Diarrhoea is common and usually mild. Keeping well hydrated is important. Oral rehydration solutions from a pharmacy can help if it is frequent. Prolonged or severe diarrhoea needs medical advice, and it may also affect how well other oral medicines, including the contraceptive pill, are absorbed.

Constipation

Constipation is especially common with orforglipron in trials and occurs with all GLP-1 medicines, partly because people eat less food and fibre. Drinking enough fluid, gradually increasing fibre and keeping active can help. A pharmacist can advise on suitable laxatives if needed.

Indigestion, reflux, burping and bloating

Slower stomach emptying can lead to reflux, heartburn, sulphurous burps and a feeling of fullness. Eating smaller meals, avoiding eating late in the evening and limiting fizzy drinks, alcohol and fatty foods can help. A pharmacist can suggest suitable antacids, but check timing with oral semaglutide, because other medicines should not be taken during the waiting period after your tablet.

Tiredness, headache and dizziness

Some people feel tired or lightheaded, particularly when eating much less than before. Making sure you eat regular, balanced meals with enough protein and fluid helps. Dizziness may also relate to lower blood pressure or dehydration, which should be discussed with a prescriber if it continues. See hydration on GLP-1 medication.

Side effects specific to tablets

Oral semaglutide: the morning routine

Oral semaglutide must be taken on an empty stomach with a small sip of water, followed by a wait (usually at least 30 minutes) before eating, drinking or taking other oral medicines. These rules exist to maximise absorption, not to reduce side effects. Breaking them is unlikely to cause harm, but it can mean the medicine works less well. For people taking other morning medicines, such as levothyroxine for an underactive thyroid, a pharmacist can help plan timings; the SmPC notes that semaglutide tablets can affect levothyroxine levels, which may need monitoring.

Orforglipron: no food rules, but still daily

Orforglipron does not have food or water restrictions, which makes the routine simpler. As a newer medicine, its full interaction profile is set out in the SmPC, which your pharmacist can check against your other medicines.

Liver safety and small-molecule GLP-1s

Two experimental small-molecule GLP-1 tablets developed by another manufacturer were discontinued during development, partly because of liver-related findings. No comparable liver safety signal was reported in the orforglipron trials published so far. As with any new medicine, monitoring continues after licensing, and the MHRA collects reports through the Yellow Card scheme.

No injection-site reactions

Tablets avoid redness, itching, bruising and lumps at injection sites, which occur with injectable GLP-1 medicines.

Less common and serious side effects

These risks apply across the GLP-1 class, including tablets.

There have also been reports of aspiration (inhaling stomach contents) during anaesthesia or deep sedation in people taking GLP-1 medicines, because food can remain in the stomach for longer. If you are due to have surgery or a procedure, tell the team that you take a GLP-1 medicine, whether tablet or injection.

The MHRA has advised that people who could become pregnant should use effective contraception while taking GLP-1 medicines and stop before a planned pregnancy, with the timing set out in each SmPC. If you become pregnant while taking one, speak to your prescriber promptly.

Mood and mental health

Regulators, including the MHRA and the European Medicines Agency, have reviewed reports of suicidal thoughts in people taking GLP-1 medicines. These reviews did not establish a causal link. However, anyone who notices a change in their mood, low mood or thoughts of self-harm while taking any medicine should seek help promptly from their GP, NHS 111 or, in an emergency, 999. Samaritans is available on 116 123.

Who is more likely to have side effects?

Side effects can affect anyone, but some factors may play a role:

• Increasing the dose too quickly. This is a key reason for the step-by-step schedule.
• Large or high-fat meals, especially early in treatment.
• Existing gut conditions, such as reflux or irritable bowel syndrome.
• Other medicines that also slow the gut or cause nausea.

People with certain conditions should not take GLP-1 medicines, or need extra caution, including those with a history of pancreatitis, a personal or family history of medullary thyroid cancer, severe gastrointestinal disease or some eating disorders. See who should not take GLP-1 medications.

Side effects and dose increases

Each dose step brings a period of adjustment. Typical schedules at the time of writing are shown below; your prescriber and the SmPC are the authority for your treatment.

Not everyone needs the highest dose. If side effects are hard to tolerate, prescribers may extend the time at a lower dose or keep you on a dose that works and is tolerable. Do not change your dose without advice.

Side effects in particular groups

People with type 2 diabetes

Foundayo is licensed for type 2 diabetes as well as weight management, and Rybelsus is licensed for diabetes only. People with diabetes who take insulin or a sulfonylurea (such as gliclazide) have a higher risk of low blood sugar when a GLP-1 medicine is added, and their prescriber may reduce those doses. Regular glucose monitoring is important when starting or increasing the dose. People with diabetic retinopathy should keep up with eye screening and report any change in vision.

Older adults

Older people may be more vulnerable to dehydration from vomiting or diarrhoea, and to dizziness or falls if they eat and drink much less than usual. Keeping fluid intake up and reporting persistent symptoms early is especially important. Older adults are also more likely to be taking several medicines, which matters for interactions and, with oral semaglutide, for the morning timing rules.

People with kidney problems

Dehydration can worsen kidney function, particularly in people with existing kidney disease. Anyone with kidney problems should seek advice quickly if they develop persistent vomiting or diarrhoea. The SmPC for each tablet sets out any cautions in kidney or liver impairment.

People with a history of eating disorders

GLP-1 medicines reduce appetite and can change people's relationship with food. They are not suitable for some people with current or past eating disorders. Prescribers should ask about this during assessment, and anyone who notices worrying thoughts or behaviours around food should talk to their GP.

A practical checklist for the first month

The first weeks of treatment, and the weeks after each dose increase, are when side effects are most likely. These general steps may help, alongside your prescriber's advice:

• Read the leaflet before your first dose, especially the instructions for taking oral semaglutide on an empty stomach.
• Plan your mornings if you take other medicines, so timing is not a daily puzzle.
• Eat smaller portions and stop at the first sign of fullness.
• Keep fluids up with regular sips through the day.
• Prioritise protein at each meal to help protect muscle; see protein on GLP-1 medication.
• Keep simple remedies to hand, after checking with a pharmacist which are suitable.
• Note your symptoms and when they happen, which helps your prescriber make adjustments.
• Know the red flags listed at the end of this guide, and when to seek urgent help.

Questions to ask your prescriber

• Which side effects are most likely with this tablet, and how long do they usually last?
• What should I do if I vomit soon after taking a dose?
• How should I time this tablet with my other medicines?
• If side effects are difficult, can I stay longer on a lower dose?
• Do I need any extra contraception, and for how long after stopping?
• Who should I contact if I have concerns between reviews?

Stopping because of side effects

If side effects are making treatment difficult, talk to your prescriber before stopping. Options may include slowing the dose increase, staying at a lower dose, adjusting your eating habits, or trying a different medicine. If you stop, weight often returns over time, as shown in withdrawal trials of the injections; see weight regain after stopping GLP-1 medication.

Ongoing costs can also influence decisions about staying on treatment. We do not quote prices, but you can see what affects cost on our prices page and compare regulated services on our provider comparison.

Reporting side effects

You can report any suspected side effect to the MHRA through the Yellow Card scheme, online or via the Yellow Card app. Reports from patients and clinicians help regulators identify new or rare problems, which is particularly important for newly licensed medicines such as GLP-1 tablets.

When to speak to a professional

Speak to your prescriber, GP or pharmacist if:

• Nausea, vomiting, diarrhoea or constipation are not settling or are affecting how much you can eat or drink
• You are unsure how to take your tablet, or how to time it with other medicines
• You are planning surgery, a procedure, or a pregnancy
• You notice hair loss, persistent tiredness or changes in mood
• You have diabetes and are taking insulin or a sulfonylurea, as doses may need adjusting

Seek urgent medical help through NHS 111, or call 999 in an emergency, if you have:

• Severe, persistent abdominal pain, especially if it spreads to the back, with or without vomiting
• Pain in the upper right abdomen with fever, or yellowing of the skin or eyes
• Vomiting or diarrhoea that stops you keeping fluids down, or signs of dehydration such as very little urine, dizziness or confusion
• Signs of a severe allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing
• Thoughts of self-harm or suicide

For more on the tablet options, visit our oral GLP-1 hub and our complete guide to oral GLP-1 medicines.