GLP-1 Side Effects

What are the most common GLP-1 side effects?

Most GLP-1 treatments, like Mounjaro, Foundayo, and the Wegovy injection and Wegovy pill, target similar hormone pathways. This means they also share similar side effects, with most of them being gastrointestinal (related to the stomach and intestines).

The most common side effects include:

• nausea
• vomiting
• diarrhoea
• constipation
• indigestion
• acid reflux
• headaches
• fatigue

If you're using weight loss injections, you might also notice mild skin irritation, like redness or swelling around your injection site. This is usually temporary and settles within a few days, especially if you rotate where you inject each week.

When do GLP-1 side effects begin?

Side effects usually start within the first few days of your first dose, or shortly after a dose increase. This is when your body is adjusting to the medication's effect on your digestion and appetite, so it's this point when you're most likely to notice symptoms.

How long do GLP-1 side effects last?

For most people, side effects ease within the first few weeks after starting treatment, as your body gets used to the medication. They may return (usually more mildly) each time your dose goes up, before settling down again.

If your side effects last longer than a few weeks or don't improve, always speak to your prescriber for advice.

Which GLP-1 treatment has the fewest side effects?

“There isn't one GLP-1 treatment that has fewer side effects than the rest, as they all work in similar ways and share a similar side effect profile. That said, oral options like the Wegovy pill and Foundayo don't carry the risk of injection site reactions, since there's no needle involved.

“Which treatment suits you best often comes down to how your own body responds, and that varies from person-to-person.”

Ian Budd, Prescribing Pharmacist at Chemist4U

Managing your GLP-1 side effects

Making some simple diet and lifestyle changes can go a long way towards managing your GLP-1 side effects, like:

• Eating smaller meals more often, instead of three large meals a day.
• Sticking to bland, low-fat foods if you're feeling sick, like toast, rice, or bananas.
• Eating more slowly and stopping as soon as you feel full.
• Staying hydrated by sipping water throughout the day.
• Avoiding lying down straight after eating.
• Moving with some gentle exercise, like a walk, to help digestion along.
• Rotating your injection site each week if you're using Mounjaro or Wegovy.

Which treatments can help with GLP-1 side effects?

If these changes aren’t quite cutting it, there are treatments available that can help to ease specific GLP-1 side effects, which we’ll outline below.

Nausea and vomiting

• Pepto-Bismol Oral Suspension: Soothes your stomach and helps to settle nausea, so you're less likely to feel or be sick.
• Pepto-Bismol Chewable Tablets: Works in the same way as the suspension, just in a more convenient tablet, ideal for on-the-go.

Diarrhoea

• Anti-Diarrhoea Capsules (Loperamide): Slows your gut down, helping to reduce diarrhoea and allow your body to absorb more fluid.
• Dioralyte Natural Sachets: Tops up the fluids and salts you lose, helping you to avoid dehydration.
• Pepto-Bismol Oral Suspension: Helps to relieve diarrhoea while also easing nausea and stomach discomfort.
• Pepto-Bismol Chewable Tablets: The same diarrhoea relief as the suspension, just in a handy tablet.

Constipation

• Senna Tablets and Senokot Laxative Tablets: Stimulates your bowel to make it easier to go.
• Laxido Sachets: Draws water into your bowel to soften stool, making them easier to pass.

Acid reflux and indigestion

• Pepto-Bismol Oral Suspension: Helps to relieve indigestion, heartburn, and feelings of stomach discomfort.
• Pepto-Bismol Chewable Tablets: Same soothing relief as the suspension, in a tablet.
• Esomeprazole Capsules: Reduces the amount of acid your stomach produces, helping to prevent and relieve frequent heartburn.
• Gaviscon Double Action Chewable Tablets: Forms a protective barrier over the stomach to help stop acid rising into the oesophagus.
• Rennie Indigestion and Heartburn Relief Tablets: Neutralises excess stomach acid quickly, for fast relief from heartburn.
• Rennie Deflatine Tablets: Eases heartburn, bloating, and trapped wind all in one go.
• BuscoMint Soft Capsules: Helps to relieve abdominal cramps, bloating, and any digestive discomfort.

Headaches

• Paracetamol: Eases headache pain so you can get on with your day.
• Ibuprofen: Tackles pain and inflammation together.
• Tiger Balm White Ointment: A cooling balm you rub into your temples that helps to ease headaches.

Skin irritation

• EMLA Cream: Numbs the skin before an injection, helping to reduce discomfort from the injection itself.

Do GLP-1s have long-term side effects?

Most GLP-1 side effects are short-lived, but a few can develop or last over a longer period of time, for example:

• Ongoing gastrointestinal symptoms: nausea or constipation can continue for some people beyond the first few weeks.
• Gallbladder problems: a small increased risk of issues like gallstones, particularly with rapid weight loss.
• Pancreatitis: rare cases of inflammation of the pancreas have been reported.

When to seek medical advice

Contact your prescriber or seek urgent medical help if you experience:

• signs of a severe allergic reaction, like swelling of the face, lips, or throat, or difficulty breathing
• severe abdominal pain that spreads to your back, which could indicate pancreatitis
• persistent vomiting or diarrhoea, or signs of dehydration
• pain in your upper right abdomen, fever, or yellowing of the skin or eyes, which could indicate a gallbladder problem
• sudden changes to your vision

Frequently asked questions about GLP-1 side effects

Who cannot take GLP-1s?

GLP-1s aren't suitable for everyone. You shouldn't take one if you:

• have a personal or family history of medullary thyroid cancer or Multiple Endocrine Neoplasia syndrome type 2
• are pregnant, breastfeeding, or planning a pregnancy
• have a known allergy to the medication

Your prescriber will always assess your full medical history before confirming if a GLP-1 treatment is safe for you.

Do GLP-1s cause hair loss?

Hair loss can happen with GLP-1 use, but it's usually linked to rapid weight loss rather than the medication itself. This is known as telogen effluvium, a temporary shedding triggered by rapid changes to your body, and it typically resolves within 3-6 months as your weight stabilises.

Sources

• Mounjaro KwikPen Patient Information Leaflet. Eli Lilly. [Accessed 8th September 2026].
• Wegovy FlexTouch Patient Information Leaflet. Novo Nordisk. [Accessed 8th September 2026].
• Wegovy Tablets Patient Information Leaflet. Electronic Medicines Compendium (eMC). [Accessed 8th September 2026].
• Foundayo Patient Information Leaflet. Electronic Medicines Compendium (eMC). [Accessed 8th September 2026].
• Adverse Effects of GLP-1 Receptor Agonists. (2015). PubMed Central (PMC). [Accessed 8th September 2026].
• Weight Loss That Lasts: Reviewing the Long-Term Impact of GLP-1 Receptor Agonists. (2025). PubMed Central (PMC). [Accessed 8th September 2026].
• Patient Information: GLP-1 Agonists and Contraception. Faculty of Sexual and Reproductive Healthcare (FSRH). [Accessed 8th September 2026].