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Guide 5 of 9 · Stage: Decide

What are the side effects of GLP-1 medicines like Ozempic and Mounjaro?

How common each one is, when it happens, what helps, and the rare problems that need a doctor straight away.

GLP Guidebook teamUpdated 12 Oct 202617 min read23 sourcesWritten from published sources
The short answer

Most people on GLP‑1 medicines like Ozempic, Wegovy and Mounjaro get stomach side effects: feeling sick, diarrhoea, vomiting or constipation. They are usually mild, come with each dose increase and fade over weeks. Serious problems such as gallstones, pancreatitis and kidney injury from dehydration are much less common, but they need urgent care. Talk to a doctor before starting, stopping or changing any medicine.

Key facts

Most common
Feeling sick, diarrhoea, vomiting, constipation1,3
How common
44 in 100 felt sick on semaglutide 2.4 mg, vs 17 in 100 on a dummy injection1
Which doses
These figures are for the weight-loss doses: semaglutide 2.4 mg (Wegovy) and tirzepatide up to 15 mg.1,3 Ozempic, the diabetes brand of semaglutide, goes up to 2 mg.9 Since 2026, UK Wegovy also comes at 7.2 mg; these figures are not for that dose.23
When
Mostly in the first 5 months, while the dose goes up. In the semaglutide trials they were most common around week 204
Stopped because of any side effect
7 in 100 on semaglutide, vs 3 in 100 on a dummy injection1
Serious, less common
Pancreatitis, gallbladder disease, kidney injury from dehydration, low sugar with some diabetes medicines2
Report a side effect
Use the MHRA Yellow Card scheme: online, in the Yellow Card app, or free on 0800 731 6789 on weekdays. How to report16

Get help now

Call 999 or go to A&E if you have any of these:

  • Severe stomach pain that won't go away, sometimes spreading to your back, with or without vomiting. This can be pancreatitis.2
  • Vomiting or diarrhoea that won't stop, or you can't keep fluids down. Losing fluid can harm your kidneys.2
  • Yellow skin or eyes, pain in your upper stomach, fever, or pale clay-coloured stools. These can be gallbladder problems.2
  • Signs of a serious allergy: swelling of the face, lips, tongue or throat, trouble breathing or swallowing, a severe rash, fainting or a very fast heartbeat.2
  • Very low blood sugar (more likely if you also take insulin, or diabetes tablets such as gliclazide or glimepiride): shaking, sweating, confusion, slurred speech or drowsiness.2
  • Sudden loss of vision, usually in one eye.8,17

See a doctor soon (within days) if you notice:

  • A lump or swelling in your neck, a hoarse voice, trouble swallowing or shortness of breath.2
  • Changes in your vision, if you have diabetes.2
  • Stomach problems or constipation that are severe or don't go away.2,3
  • Low mood, or thoughts that are new, worse, or worry you.5

Need help fast, but it's not an emergency? Use NHS 111 online or call 111 in England, NHS 111 Wales in Wales, or NHS 24 on 111 in Scotland.21 Northern Ireland has no 111 service: call your GP surgery, or the GP out-of-hours service in the evening and at weekends.22 Take the medicine box or leaflet with you, so the doctor knows exactly what you are on.17

On this page
  1. What are the common side effects?
  2. When do they start, and how long do they last?
  3. What helps with nausea and other stomach effects?
  4. Side effects at a glance
  5. What are the serious risks?
  6. Will I lose muscle? And what is "Ozempic face"?
  7. How can they affect eating and mood?
  8. Are fake or unregulated products a risk?
  9. How do I report a side effect in the UK?
  10. Questions people ask

What are the common side effects?

Stomach and gut effects. In the main semaglutide weight trial (STEP 1, about 2,000 adults over 68 weeks), 74 in 100 people had at least one, compared with 48 in 100 on a dummy injection.1

The most common are feeling sick (nausea), diarrhoea, vomiting and constipation.1 Other effects include stomach pain, heartburn (reflux), burping, bloating and tiredness.2

A dummy injection (placebo) contains no medicine. People on it get some stomach symptoms too. So the real effect of the medicine is the difference between the two numbers.

Out of every 100 people, how many felt sick (nausea) at some point:

STEP 1Semaglutide 2.4 mg, weekly

About 2,000 adults, 68 weeks.1

Semaglutide44 in 100
Dummy injection17 in 100

So about 27 in 100 felt sick because of the medicine itself.

US labelTirzepatide 15 mg, weekly

Weight trials summarised on the US label, up to 72 weeks.3

Tirzepatide28 in 100
Dummy injection8 in 100

So about 20 in 100 felt sick because of the medicine itself.

Most of these effects are mild or moderate. In the semaglutide trials, 98 in 100 stomach side effects were mild or moderate.4 Still, 7 in 100 people stopped semaglutide because of side effects, compared with 3 in 100 on the dummy injection.1 For tirzepatide 15 mg, it was about 7 in 100, compared with 3 in 100.3

Don't compare these numbers across medicines. The semaglutide and tirzepatide figures come from different trials, with different people. They don't show which medicine is gentler.

When do they start, and how long do they last?

They build up while the dose is going up, and are most common around the time you reach the full dose. Each bout usually lasts about a week or less. Constipation is the exception.4

You start on a low dose and go up in steps, usually every 4 weeks. Going up slowly lowers the risk of stomach side effects.2,3 The diagram shows what the semaglutide trials found.4

Your doctor sets your dose. These steps are from the US labels. Semaglutide (Wegovy) goes 0.25 → 0.5 → 1 → 1.7 → 2.4 mg, one step every 4 weeks.2 Tirzepatide starts at 2.5 mg and rises 2.5 mg at a time, after at least 4 weeks on each dose.3
  1. Month 1Weeks 1–4
    Starting doseStomach effects can begin.4
  2. Months 2–4Weeks 5–16
    Dose goes up every 4 weeksNausea, diarrhoea and vomiting become more common with each step. Most people who stopped did so in the first few months.3,4
  3. Month 5Weeks 17–20
    Full dose reachedIn the semaglutide trials, nausea, diarrhoea and vomiting peaked at about week 20, then fell.4
    Peak
  4. Month 6 onSteady dose
    Most people settleStomach effects become less common. Constipation can linger. A small number keep having effects throughout.4
  5. Over monthsAs weight drops
    Effects of the weight loss itselfGallstones and hair loss are linked to losing weight, especially quickly.2,3

Bars are a rough picture of how common stomach effects are, not exact numbers. Based on the main semaglutide 2.4 mg weight trials (STEP 1–3), pooled, and Mounjaro's US label (sold there as Zepbound).3,4

8 daystypical length of a bout of nausea on semaglutide4
3 daystypical bout of diarrhoea
2 daystypical bout of vomiting
47 daystypical bout of constipation

These are medians: half of bouts were shorter, half longer.4 One more useful finding: people with stomach side effects lost about the same weight as people without them. Feeling sick isn't what makes the medicine work.4

What helps with nausea and other stomach effects?

Smaller meals, less fatty food and enough fluids help most. If a dose step is too hard, your doctor can slow the next one down.

An expert advisory from four US obesity and nutrition societies suggests these steps:5

  • Eat smaller meals, more often. Nausea often comes in the morning or after a long gap without food. A small breakfast, then small meals every 3–4 hours, can help.5
  • Go easy on fatty and heavy food, especially in the first days after a dose step. Large or high-fat meals can also bring on diarrhoea.5 That might mean fewer fried foods, pastries, takeaways or creamy sauces for a while.
  • Drink enough fluids. This helps with constipation, and protects your kidneys if you're vomiting or have diarrhoea.2,5
  • Get fibre from food, like vegetables, fruit and whole grains, for constipation.5
  • Try ginger or peppermint tea for nausea.5
  • Keep alcohol low. It can make nausea and heartburn worse.5

Slower dose steps are a doctor's call. The Wegovy label says that if a dose step isn't tolerated, the doctor can consider waiting another 4 weeks before going up.2 Some people do better on a slower schedule.5 Don't change your dose on your own.

Doctors can also prescribe anti-nausea or constipation medicines if food changes aren't enough.5

Side effects at a glance

How often each common side effect happened on the medicine and on a dummy injection, and what to do about it.

Feeling sick (nausea)

Semaglutide44% vs 17%1
Tirzepatide28% vs 8%3
When
After dose steps; bouts last about 8 days4
What to do
Small meals, less fatty food, ginger tea5

Diarrhoea

Semaglutide32% vs 16%1
Tirzepatide23% vs 8%3
When
After dose steps; about 3 days4
What to do
Avoid large, high-fat meals; drink fluids5

Vomiting

Semaglutide25% vs 7%1
Tirzepatide13% vs 2%3
When
After dose steps; about 2 days4
What to do
Sip fluids. Can't keep them down? Get help2

Constipation

Semaglutide23% vs 10%1
Tirzepatide11% vs 5%3
When
Lasts longest; about 47 days4
What to do
Fluids and fibre from food; ask about a laxative5

Heartburn (reflux)

Semaglutide5% vs 3%2
Tirzepatide5% vs 2%3
When
Any time
What to do
Smaller meals, less alcohol5

Tiredness

Semaglutide11% vs 5%2
Tirzepatide7% vs 3%3
When
Any time
What to do
If it doesn't lift, tell your doctor: it can be a sign of low nutrients5

Injection-site redness or itch

Semaglutide5% vs 7%1
Slightly more common on the dummy injection in this trial
Tirzepatide8% vs 2%3
When
After a dose
What to do
Use a different spot each week2

Hair loss

Semaglutide3% vs 1%2
Tirzepatide5% vs 1%3
When
As weight drops3
What to do
See hair loss below

Semaglutide: the main weight trial (STEP 1), 68 weeks (nausea, diarrhoea, vomiting, constipation, injection site); other rows from the Wegovy label's pooled trials. Tirzepatide: Mounjaro's US label (sold there as Zepbound), which pools two weight trials (SURMOUNT-1 and -2), up to 72 weeks. Rounded to whole numbers.1,2,3

What are the serious risks?

They are rare, but you should know the warning signs. Most come from the drug labels' official warnings.

The numbers below are from trials, compared with a dummy injection where possible. "Per 100 patient-years" means the number of cases if 100 people took the medicine for one year.

Inflamed pancreas (pancreatitis) Uncommon

The pancreas is a gland behind your stomach. In Wegovy's weight trials, pancreatitis was confirmed in 0.2 cases per 100 patient-years, vs under 0.1 on the dummy injection.2 Put another way: if 1,000 people took it for a year, about 2 would get pancreatitis, compared with under 1 on the dummy injection. Severe cases can be fatal.2 The European Ozempic label lists it as "uncommon": between 1 in 1,000 and 1 in 100 people.9 In January 2026, the MHRA updated the product information for all GLP-1 medicines on the small risk of severe acute pancreatitis.19

Watch for: severe stomach pain that won't go away, sometimes reaching your back. Get help now.2

Gallstones and gallbladder disease Common

In the main semaglutide weight trial (STEP 1), gallbladder problems (mostly gallstones) affected 2.6% on semaglutide vs 1.2% on the dummy injection.1 That is about 26 in every 1,000 people, vs 12 in 1,000. The European Ozempic label lists gallstones as "common": between 1 in 100 and 1 in 10 people.9 On tirzepatide, an inflamed gallbladder affected 0.7% vs 0.2%.3 Losing weight fast raises the risk on its own. Some cases need surgery.2

Watch for: upper stomach pain, fever, yellow skin or eyes, pale stools.2

Dehydration and kidney injury Less common

Vomiting and diarrhoea can drain fluid from your body. That can damage the kidneys suddenly. Doctors call this acute kidney injury. Some people have needed dialysis.2 In tirzepatide's trials, it affected 0.5% vs 0.2% on the dummy injection.3 The risk is higher if your kidneys are already weak.2

Vomiting or diarrhoea that won't stop: drink fluids and tell your doctor straight away.2

Low blood sugar (hypoglycaemia) If you have diabetes

Low sugar is mainly a risk for people with diabetes. It is higher if you also take insulin or a sugar pill from the sulfonylurea group, such as glimepiride or gliclazide.2 In people with type 2 diabetes, low sugar happened in 6.2% on Wegovy vs 2.5% on the dummy injection.2 That is about 62 in every 1,000 people, vs 25 in 1,000. Your doctor may lower the dose of your insulin or sugar pill when you start.2

Know the signs: shaking, sweating, dizziness, hunger, fast heartbeat, confusion. Check your sugar as your doctor advises.2

Thyroid tumour warning Unknown in humans

In rats and mice, these medicines caused tumours of certain thyroid cells, called C-cells. Nobody knows yet if they do this in people.2,3 The US labels carry their strongest ("boxed") warning about it.2

The US label says not to take them if you or a family member has had medullary thyroid cancer, a rare type of thyroid cancer, or if you have MEN 2 (multiple endocrine neoplasia type 2), a rare inherited condition that causes gland tumours. Tell your doctor if this applies.2 Routine blood tests or scans to check for it are of uncertain value.3

See a doctor soon for: a lump or swelling in the neck, a hoarse voice, trouble swallowing or breathing.2

Diabetic eye disease getting worse If you have diabetes

In a heart-safety trial of semaglutide in people with type 2 diabetes (SUSTAIN-6), serious eye complications happened in 3.0% on semaglutide vs 1.8% on the dummy injection.6,2 That is about 30 in every 1,000 people, vs 18 in 1,000. The extra risk was bigger in people who already had eye damage: 8.2% vs 5.2%, or about 82 vs 52 in 1,000.2 A fast drop in blood sugar can make eye disease worse for a while.2

If you have diabetic eye disease, keep up your eye checks.2

Sudden vision loss (NAION) Very rare

NAION (non-arteritic anterior ischaemic optic neuropathy) is a sudden loss of blood flow to the nerve at the back of the eye. In June 2025, Europe's medicine regulator (EMA) listed it as a "very rare" side effect of semaglutide: up to 1 in 10,000 people.8 Studies suggest about 1 extra case per 10,000 people with diabetes treated for a year.9

Sudden loss of vision or fast-worsening eyesight: contact a doctor without delay.8

Allergic reactions Serious ones are rare

Serious allergic reactions (anaphylaxis) and swelling under the skin (angioedema) have been reported.2 Milder reactions are more common: 5% on tirzepatide vs 3% on the dummy injection, mostly rash and itching.3

Swelling of face, lips or throat, or trouble breathing: get help now.2

Surgery, sedation and endoscopy Rare

These medicines slow your stomach. There are rare reports of food coming back up into the lungs (aspiration) under general anaesthesia or deep sedation, even after fasting.2 It isn't known whether stopping the medicine first lowers this risk.2

Before any surgery or procedure, tell every doctor that you take a GLP‑1 medicine.2

Blocked or very slow gut (ileus, gastroparesis) Rare

Since these medicines went on sale, there have been reports of a stalled gut (ileus), blocked bowel and severe constipation.2,3 They aren't recommended if you already have severe gastroparesis, a condition where the stomach empties very slowly.3

A 2023 study of US health records found a higher risk of gastroparesis on semaglutide than on another weight-loss medicine, bupropion–naltrexone: 9.1 vs 3.1 cases per 1,000 people a year.10 Studies like this can't prove the medicine caused it.

Less common effects on the Wegovy label

Out of every 1,000 people in the trials, how many had each one on Wegovy, against a dummy injection:2

  • Low blood pressure: 13 in 1,000 on Wegovy, against 4 on a dummy injection. It often follows fluid loss from vomiting or diarrhoea.2
  • Fainting: 8 in 1,000, against 2.2
  • Changes in taste: 17 in 1,000, against 5.2
  • A slightly faster resting heartbeat: up by 1–4 beats a minute on average.2

Will I lose muscle? And what is "Ozempic face"?

Some of the weight you lose is muscle. Eating enough protein and doing strength exercise help protect it.

In the main semaglutide weight trial (STEP 1), people lost 13.6 kg on average. About 8.3 kg (62%) was fat and 5.3 kg (38%) was lean mass.5 Lean mass is everything that isn't fat, including water and organs. Muscle is about half of it, so roughly 1 kg in every 5 kg lost is muscle.5

That's similar to other ways of losing a lot of weight fast, such as surgery or very low-calorie diets.5

What the 13.6 kg lost in STEP 1 was made of, on average5
8.3 kg~2.7 kg~2.6 kg
FatMuscle (about half the lean mass)Other lean mass: water, organs

So roughly 1 kg in every 5 kg lost is muscle.

How to protect your muscle

  • Strength training. Exercise against resistance, like weights, bands or body-weight moves, helps keep muscle. Walking alone helps less.5
  • Protein at every meal. Experts have proposed 1.2–1.6 g of protein per kg of body weight a day while losing weight, above the usual 0.8 g. For a 70 kg person, that is about 85–110 g a day. The right target for each person isn't settled.5 Options include eggs, Greek yoghurt, fish, chicken, beans and lentils. If you have kidney disease, ask your doctor before eating more protein. Guide 8 has more on eating.

"Ozempic face"

This isn't a medical diagnosis. It's a popular name for a face that looks thinner, older or saggier after quick weight loss.11 A 2026 review linked it to losing fat from the face, plus thinner and less stretchy skin.11

Illustration of the same made-up woman twice: a fuller face before, then a slimmer face with fine lines and loose skin at the jaw and neck after fast weight lossIllustration of the same made-up man twice: a fuller face before, then a slimmer, more lined face with looser skin at the neck after fast weight loss
  1. Less fat under the skinThe face loses volume and looks thinner.11
  2. Thinner skinWith less collagen and elastin, the fibres that keep skin firm.11
  3. Less stretchSkin doesn't shrink back, so loose folds form and the face can look older.11
Illustrations of made-up people, not photos of real ones.

Older age, losing weight quickly, not drinking enough and too little protein made it worse. The review suggests slower weight loss, good nutrition and fluids.11

Hair loss

Hair thinning was reported in about 3% on Wegovy vs 1% on the dummy injection.2 On tirzepatide, it was 7% of women and under 1% of men.3 The labels link it to the weight loss. No one on tirzepatide in the trials stopped because of it.3 Heavy hair loss can also be a sign of low nutrients, so mention it to your doctor.5

How can they affect eating and mood?

Many people think about food less. Some also enjoy food less. If you have had an eating disorder, these medicines need extra care.

"Food noise" often goes quiet. Studies show less constant thinking about food, less emotional eating and fewer binges.5

Food can feel less enjoyable. For some people, this lowers their quality of life, and some stop the medicine because of it.5

Eating disorders. The effect of these medicines on anorexia, bulimia or binge eating isn't well known. They could make symptoms better or worse.5 Experts advise screening before starting, and a specialist if you have a history of an eating disorder.5

Suicidal thoughts. Regulators have reviewed this. In April 2024, Europe's regulator found that the evidence does not support a link between these medicines and suicidal thoughts or self-harm.7 In early 2026, the US removed this warning from the Wegovy and Zepbound labels (Zepbound is the US name for Mounjaro).2,3

That doesn't mean mood never changes. Experts still advise checking for depression before starting.5 If your mood drops or you have thoughts of harming yourself, talk to a doctor. If you are in danger, call 999.

Are fake or unregulated products a risk?

Yes, including in the UK. Fake pens and illegal products can contain the wrong dose, the wrong medicine, or nothing at all.

In June 2024, the World Health Organization (WHO) warned about fake Ozempic found in Brazil, the UK and the US. It said reports of fake semaglutide have risen in all regions since 2022.12 Some fakes may contain hidden insulin, which can push blood sugar dangerously low.12

In the UK.
  • In October 2023, the MHRA, the UK medicines regulator, warned that fake Ozempic and Saxenda pens had been found here.14
  • In February 2026, it warned that a fake Mounjaro KwikPen 15 mg, batch D873576, had been supplied through one UK online pharmacy. It was spotted because the dose knob came off while in use.15
  • In October 2025, it found the UK's first illegal factory making weight-loss pens, in Northampton, and seized more than 2,000 unlicensed retatrutide and tirzepatide pens.20 Retatrutide is not licensed in the UK.

The MHRA says products sold as a powder in a vial, which you mix with liquid before injecting, are not authorised.18 It also says never to buy these medicines from beauty salons or through social media.18 In the US, the FDA has had reports of people hospitalised after measuring the wrong dose of unapproved semaglutide themselves.13

Get them only with a prescription, from a pharmacy you can check on the official register. Guide 6 explains how to check a pharmacy, and the checks an online service must make before prescribing.

How do I report a side effect in the UK?

Tell your doctor or pharmacist. You can also report it yourself to the Yellow Card scheme, which the MHRA runs. The MHRA asks patients to report GLP-1 side effects directly to it.18,16

  • Online, on the Yellow Card website (yellowcard.mhra.gov.uk). This is the quickest way.16
  • In the Yellow Card app, from the Apple App Store or Google Play.16
  • By phone, free, on 0800 731 6789, on weekdays from 9am to 5pm.16
  • On a paper form, from pharmacies and GP surgeries.16

Before you report, note the brand, strength and batch number from the box. If you think your pen is fake, report that too, and keep the pen and its packaging.15

Questions people ask

Before you start

Do GLP-1 medicines cause thyroid cancer?

They caused thyroid tumours in rodents. It's not known whether they do in people.2 The US label says people with a personal or family history of medullary thyroid cancer, or with MEN 2, shouldn't take them; tell your doctor if this applies.2

Does Mounjaro cause fewer side effects than Ozempic?

You can't tell from the numbers on this page. They come from separate trials with different people and doses. Both cause the same kinds of stomach effects, mostly during dose steps.2,3

Is it safe if I'm planning a pregnancy or take the pill?

The MHRA says to stop semaglutide at least 2 months, and tirzepatide at least 1 month, before trying to get pregnant.18 Tirzepatide can make the contraceptive pill less reliable. The MHRA advises adding a barrier method, such as a condom, for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.18 Guide 4 has more.

Once you're taking it

Will the side effects go away?

For most people, yes. In the semaglutide trials, stomach effects peaked around week 20 and fell after that. A small number had them throughout.4

Do I lose more weight if I feel sick?

No. People with and without stomach side effects lost about the same weight on semaglutide.4

I missed doses. Can I restart at my old dose?

Not always. The Wegovy label says: if you miss one dose and your next dose is more than 2 days away, take it as soon as you can. If it is less than 2 days away, skip it and take the next one on your usual day. If you miss 2 or more weekly doses in a row, restart at a lower dose and step up again. This lowers the risk of stomach side effects.2 Ask your doctor which dose to restart on. Guide 8 covers missed doses in full.

I have surgery or an endoscopy coming up. What should I do?

Tell the surgeon, the anaesthetist and the doctor doing the procedure that you take a GLP‑1 medicine. They will decide what to do.2

Before you move on

  • Stomach side effects are common, usually mild, and worst while the dose goes up.
  • Small meals, less fatty food and enough fluids help. Slower dose steps are your doctor's call.
  • You know the "get help now" signs: severe stomach pain, vomiting you can't stop, yellow skin, allergy, very low sugar.
  • The US label rules them out with a personal or family history of medullary thyroid cancer, or with MEN 2: tell your doctor.
  • Protein and strength training help protect muscle.
  • You can report a side effect through the Yellow Card scheme.
Should I consider a GLP-1?Life on a GLP-1Stopping and the long term
Was this guide easy to understand?

Sources

  1. Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). NEJM 2021;384:989–1002. doi:10.1056/NEJMoa2032183
  2. US FDA. Wegovy (semaglutide) prescribing information and Medication Guide, revised June 2026 (US label). DailyMed
  3. US FDA. Zepbound (tirzepatide; sold in the UK as Mounjaro) prescribing information, revised August 2026 (US label). FDA PDF
  4. Wharton S et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity (STEP 1–4). Diabetes, Obesity and Metabolism 2022;24:94–105. doi:10.1111/dom.14551
  5. Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory (ACLM, ASN, OMA, The Obesity Society). American Journal of Clinical Nutrition 2025;122:344–367. Declared interests: 4 of 18 authors declare advisory or speaker roles with Novo Nordisk and 5 with Eli Lilly (paper's own declaration). doi:10.1016/j.ajcnut.2025.04.023
  6. Marso SP et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6). NEJM 2016;375:1834–44. doi:10.1056/NEJMoa1607141
  7. European Medicines Agency. PRAC meeting highlights, 8–11 April 2024 (GLP-1 receptor agonists and suicidal thoughts). 12 April 2024. EMA
  8. European Medicines Agency. PRAC meeting highlights, 2–5 June 2025 (semaglutide and NAION). 6 June 2025. EMA
  9. European Medicines Agency. Ozempic: summary of product characteristics (EU label), section 4.8. EMA PDF
  10. Sodhi M et al. Risk of gastrointestinal adverse events associated with GLP-1 receptor agonists for weight loss. JAMA 2023;330:1795–7. doi:10.1001/jama.2023.19574
  11. Barone M et al. Effects of GLP-1 receptor agonists on skin quality: a comprehensive literature review. Aesthetic Plastic Surgery 2026;50:5403–7. doi:10.1007/s00266-026-05820-4
  12. World Health Organization. WHO issues warning on falsified medicines used for diabetes treatment and weight loss (Medical Product Alert 2/2024). 20 June 2024. WHO
  13. US FDA. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Page dated 1 October 2026. FDA
  14. MHRA. MHRA warns of unsafe fake weight loss pens. 26 October 2023. GOV.UK
  15. MHRA. Drug Safety Update: falsified Mounjaro (tirzepatide) KwikPen 15 mg pre-filled pens (batch D873576; "the dose knob came off while in use"). 24 February 2026. GOV.UK
  16. All Wales Therapeutics and Toxicology Centre (Yellow Card Centre Wales, NHS Wales). Yellow Card reporting for patients, carers and the public (online, app, freephone 0800 731 6789 on weekdays 09:00 to 17:00, paper forms). Checked 12 October 2026. NHS Wales · Yellow Card
  17. NHS. Semaglutide: side effects. Page last reviewed 15 May 2026. NHS
  18. MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know (report side effects to the Yellow Card scheme; pregnancy and contraception; powder-in-vial products not authorised; don't buy from beauty salons or social media). Published 5 June 2025, updated 5 February 2026. GOV.UK
  19. MHRA. MHRA updates guidance for GLP-1 prescribers and patients (product information updated on "the small risk of severe acute pancreatitis"). 29 January 2026. GOV.UK
  20. MHRA. MHRA smashes major illicit weight loss medicine production facility in record seizure (Northampton; "more than 2,000 unlicensed retatrutide and tirzepatide pens"). 24 October 2025. GOV.UK
  21. NHS. When to use 111 (NHS 111 in England; NHS 24 111 in Scotland; NHS 111 Wales; "If you have signs of a life-threatening illness… call 999 now"). Checked 12 October 2026. NHS
  22. nidirect (Northern Ireland). GP out-of-hours service. Checked 12 October 2026. nidirect
  23. MHRA. Single-dose 7.2 mg semaglutide (Wegovy) pen approved to treat adult patients with obesity (follows the January 2026 authorisation of the 7.2 mg weekly dose). 14 April 2026. GOV.UK

Last checked 12 Oct 2026 · Next review due Jan 2027 · Report an error

How this guide was made. Written by the GLP Guidebook team from the sources above: drug labels, published trials, MHRA and NHS notices. Label figures come from the US and European labels, which are published in full and easy to check; your UK pack leaflet is the version that applies to you. It's general information, not medical advice. Talk to a qualified doctor before starting, stopping or changing any medicine. In an emergency, call 999. How we write