Serious Side Effects of the Wegovy Pill: What to Watch For

How safe is the Wegovy pill overall?

The Wegovy pill is safe for most people who take it. Serious side effects of the Wegovy pill are not commonly reported. 

Oral Wegovy is a glucagon-like peptide-1 (GLP-1) weight-loss drug. It contains the active ingredient semaglutide. The Medicines and Healthcare products Regulatory Agency (MHRA) approved oral Wegovy for UK use in June 2026. This makes it the first GLP-1 weight-loss tablet available here. 

Like other GLP-1 medications, Wegovy tablets work by reducing appetite and helping to quieten food cravings. Combining treatment with a healthy, balanced diet and increased physical activity brings the best long-term outcomes.

Several large clinical trials have studied the pill’s effectiveness and safety. In the OASIS 4 trial, 205 adults took the 25 mg tablet for 64 weeks. Serious side effects were reported by 3.9% of them. The rate was higher (8.8%) in the placebo group, which took an inactive pill for comparison.

Around 7% of people stopped treatment with the active Wegovy tablet because of side effects. This compares closely to the 6% who stopped taking the placebo.

Most side effects of Wegovy are digestive and are linked to how the medicine slows your stomach and gut movement. These common side effects include nausea, vomiting, diarrhoea and constipation. Symptoms usually appear when you first start treatment or after a dose increase and settle as your body adjusts a few weeks later. People are most likely to need support during their first few weeks of treatment. 

Serious risks are much less common and often less familiar than the digestive Wegovy pill side effects. A handful of conditions can increase these risks, such as a history of gallstones, gastroparesis or kidney disease. Answering your consultation fully and honestly is important so that a prescriber can assess your risk accurately.

The injectable form has a longer safety track record as there are more years of real‑world safety data related to the injection compared to the tablet so we can say  Wegovy is safe as a weekly injection. 

Can the Wegovy pill cause pancreatitis?

The Wegovy pill’s pancreatitis (inflammation of the pancreas) risk is low, but not zero. In the OASIS 4 tablet trial itself, no one on the 25 mg pill developed acute pancreatitis. About 1% of the placebo group did, though with only around 100 people on placebo, that is a single case. Across the larger injection trials, roughly 1 in 500 people on semaglutide developed acute pancreatitis.

The MHRA strengthened its pancreatitis warning across all GLP-1 medicines in January 2026. This followed a small number of severe cases, including rare life-threatening ones. How much the drug itself adds to that risk is still debated. Being aware of the the warning signs is what matters:

• severe, ongoing stomach pain that spreads through to your back. It does not ease, and it often feels worse after eating or when you lie down. 
• nausea and vomiting
• bloating and/or a lost appetite 
• fever, fast breathing or a racing heartbeat. 

If pain like that comes on suddenly, with or without the rest, call 999 or go to A&E and stop taking the Wegovy pill.

Can the Wegovy pill cause gallbladder problems?

Gallstones become more likely on the Wegovy pill, mostly because losing weight quickly is itself a trigger. Your gallbladder is a small pouch under your liver that stores bile to help with digestion. Gallstones form when bile hardens into small, stone-like pieces. Sometimes these can be as tiny as grains of sand, and sometimes larger, like small pebbles.  

Losing weight quickly makes gallstones more likely. This can happen with rapid weight loss in general, whether it’s through diet changes, surgery, or medicines such as GLP‑1 treatments 

In the OASIS 4 trial, gall bladder disease including gallstones affected 2.5% of people on the tablet, roughly 1 in 40. 

Gallstones do not always cause symptoms, and many people never know they have them. The ones to act on bring severe pain in the upper right of your stomach. This may be with or without vomiting, yellowing of your skin or the whites of your eyes, or a fever.

Does the Wegovy pill cause thyroid cancer?

The UK licence for the Wegovy pill does not list thyroid cancer as a reason to avoid it. Worries about the Wegovy pill and thyroid cancer come from the US label. The UK regulator takes a different view.

In the United States, the Food and Drug Administration (FDA) places a boxed warning on semaglutide about thyroid tumours. This warning is based on studies in rats, where semaglutide caused thyroid C‑cell tumours, including medullary thyroid carcinoma (MTC). In humans, it’s not known whether semaglutide causes these tumours 

Human thyroid tissue appears to have very low levels of the GLP‑1 receptor. Because of this, experts think the risk to people is likely to be low. In clinical studies of semaglutide, thyroid cancer has been rare. 

A review of the trials found it in fewer than 1 in 100 people, with no clear increase over placebo. The UK prescribing information does not carry the boxed warning. 

We still take your thyroid history into account when assessing the suitability of oral Wegovy for you. Tell us if you or a close relative has had MTC or multiple endocrine neoplasia syndrome type 2 (MEN2). If you are taking the medication, report a new neck lump, a hoarse voice or trouble swallowing immediately. The full list of who should not take the Wegovy pill covers a few other conditions.

Can the Wegovy pill affect your kidneys?

Dehydration is the main way the Wegovy pill can affect your kidneys. Heavy vomiting or diarrhoea can leave you short of fluid.

In rare cases, dehydration reduces how well your kidneys work for a while. Staying hydrated is the main protection. That matters most in the first few weeks or when digestive side effects peak.

People searching for the Wegovy pill and kidney disease usually worry about lasting damage. However, the real short-term risk is simply fluid loss.

Can the Wegovy pill affect your mood?

Regulators have looked at the Wegovy pill and links to mood changes. They found no evidence that the Wegovy pill causes suicidal thoughts. In 2024, the MHRA reviewed the evidence. 

It found nothing to suggest GLP-1 weight loss medications cause an increase in suicidal or self-harming thoughts. European regulators reached the same conclusion.

One 2024 study of the World Health Organization’s safety database raised a flag from patient reports. It found that suicidal thoughts were about 45% more likely to be reported for semaglutide than for other medicines overall.

These reports were rare, a small fraction of all side effects logged for semaglutide. These thoughts were strongest in people already taking antidepressants. It hints that existing mental health conditions may explain part of it.

If you have a history of depression or anxiety, you can reach out to us if needed to discuss any concerns around your medication. 

Can the Wegovy pill cause a serious allergic reaction?

Serious allergic reactions to the Wegovy pill are rare, but they are an emergency when they happen. Reactions like anaphylaxis and a deeper swelling of the skin called angioedema affect fewer than 1 in 1,000 people. Most people never have any allergic reaction at all.

The signs are swelling of your face, lips or throat, trouble breathing, or a sudden widespread rash, you need to call 999 immediately. Caught early, anaphylaxis responds well to treatment.

Does the Wegovy pill affect your heart and cardiovascular health?

The Wegovy pill cardiovascular safety profile looks reassuring, not concerning. In some people who already have existing heart disease, semaglutide can reduce the risk of heart attack or stroke. That evidence comes from the injection, tested in the SELECT trial, rather than the tablet.

One group of patients are missing from the evidence entirely: people with severe (advanced) heart failure. The Wegovy pill has not been tested in them, so let us know if this applies to you. 

Other common safety questions

Can the Wegovy pill cause gastroparesis?

It doesn’t cause gastroparesis in most people, but it can worsen symptoms in people who already have it.

Both gastroparesis and semaglutide involve slower stomach emptying. This slowing is part of how semaglutide works. Helping people feel full sooner and for longer, which can reduce appetite and support weight loss

In people with gastroparesis, where the stomach empties too slowly, this can make symptoms worse. Prescribing guidance does not recommend the pill when the condition is severe. Tell us if you have it.

Does the Wegovy pill help or harm sleep apnoea?

Sleep apnoea is not a side effect of oral Wegovy treatment. The Wegovy pill sleep apnoea link is mainly related to losing weight, not a direct treatment effect. A large 2026 study looked at around 380,000 real-world semaglutide users. They were roughly 38% less likely to develop new sleep apnoea.

If you use a CPAP machine, the mask that holds your airway open at night, keep using it. Any decision to change or stop CPAP should be made with the team managing your sleep apnoea and not just because you’ve started the pill.

Is it safe to take Wegovy with levothyroxine or warfarin?

Yes, but you may need closer monitoring of both. The Wegovy pill and levothyroxine can interact because semaglutide can raise the level of levothyroxine in your blood. Your thyroid results may need checking, and your levothyroxine dose adjusted if needed. 

Warfarin needs similar care. Semaglutide does not change how warfarin works in any meaningful way, but your INR should be checked more often. This applies especially when you begin treatment or change your dose. 

INR is the blood test that shows how quickly your blood clots, and it guides your warfarin dose. Tell us and whoever looks after your warfarin before you start.

Does the Wegovy pill interact with the contraceptive pill?

No, the Wegovy pill does not reduce how well the contraceptive pill works. Keep using effective contraception while you take the Wegovy pill, because it should not be used during pregnancy. If you are planning to try for a baby, stop the pill at least 2 months beforehand, since semaglutide leaves the body slowly. 

When should I see a doctor?

Most side effects are mild and settle on their own. This next section covers the side effects that may not, and explains what to look out for and what to do if they happen.  

Symptom	What it may mean	What to do
Ongoing mild nausea, vomiting, diarrhoea or constipation you can still manage	Common early side effects	Message our clinical team for support
Heartburn, reflux, or changes in your appetite	Usually mild and settle	Message our clinical team for support
Yellowing of your skin or the whites of your eyes, severe upper-right stomach pain, or a fever	Possible gallbladder problem, including acute cholecystitis	GP the same day, or NHS 111 Stop the pill
A new lump in your neck, a hoarse voice, or trouble swallowing	This could be a sign of a thyroid problem and should be checked.	GP the same day, or NHS 111 Stop the pill
Vomiting or diarrhoea so bad you cannot keep fluids down for over 6 hours	Risk of dehydration	GP the same day or NHS 111 Stop the pill
Severe stomach pain spreading to your back, with nausea or vomiting	Possible pancreatitis	Call 999 or go to A&E Stop the pill
Sudden changes in vision, including loss of vision in one eye	A rare eye condition called NAION	Call 999 or go to A&E Stop the pill
Swelling of your face, lips or throat, trouble breathing, or a sudden rash	Serious allergic reaction	Call 999Stop the pill
Barely passing urine, dizziness, or confusion	Severe dehydration	999 or A&E

If you ever feel you might act on thoughts of harming yourself, treat it as an emergency. Go to A&E and ask for the CRISIS team. 

Key takeaways

• Serious side effects are uncommon. In OASIS 4, they were less frequent on the tablet (3.9%) than on placebo (8.8%).
• Pancreatitis and gallbladder problems are two serious side effects with clear warning signs, so it’s important to know what symptoms to look out for.
• The UK licence does not treat thyroid cancer as a reason to avoid the pill, unlike the US label. In the trials,  thyroid cancer stayed under 1%. 
• Tell us first if you have a history of depression, anxiety, gallstones, gastroparesis or kidney disease.
• Most side effects are digestive and settle within a few weeks of starting the Wegovy pill or after a dose increase.

References

Oral Semaglutide at a Dose of 25 mg in Adults with Overweight or Obesity (OASIS 4), New England Journal of Medicine, 2025 [Accessed 6 July 2026].

Wegovy 25 mg tablets: Summary of Product Characteristics, electronic medicines compendium (emc), 2026 [Accessed 6 July 2026].

Wegovy (semaglutide) tablets: Prescribing Information (NDA 218316), US Food and Drug Administration, 2025 [Accessed 6 July 2026]. 

First GLP-1 tablet for weight loss approved in the UK, GOV.UK (MHRA), 2026 [Accessed 6 July 2026].

GLP-1 receptor agonists and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis, including necrotising and fatal cases, GOV.UK Drug Safety Update, 2026 [Accessed 6 July 2026].

Acute pancreatitis, NHS, 2026 [Accessed 6 July 2026]. 

Gallstones, NHS, 2026 [Accessed 6 July 2026]. 

Acute cholecystitis, NHS, 2026 [Accessed 6 July 2026].

Effects of Semaglutide on Obstructive Sleep Apnea Risk and Outcomes in Patients with Obesity, Annals of the American Thoracic Society, 2026 [Accessed 6 July 2026]. 

MHRA Safety Roundup: February 2026, GOV.UK, 2026 [Accessed 6 July 2026].

MHRA finds evidence does not support a link between GLP-1 receptor agonists and suicidal and self-injurious thoughts and actions, GOV.UK, 2024 [Accessed 6 July 2026].

Disproportionality Analysis From World Health Organization Data on Semaglutide, Liraglutide, and Suicidality, JAMA Network Open, 2024 [Accessed 6 July 2026].

Assessment of Thyroid Carcinogenic Risk and Safety Profile of GLP-1 RA Semaglutide, PMC (National Library of Medicine), 2024 [Accessed 6 July 2026].

Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT), New England Journal of Medicine, 2023 [Accessed 6 July 2026]. 

Sleep apnoea, NHS, 2026 [Accessed 6 July 2026].

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