Rare but serious GLP-1 risks

Made with AI tools and overseen by an Australian GP · Updated 8 November 2026

Rare means rare, not never. Knowing the warning signs matters more than doom-scrolling the side-effect list.

Quick answer: Serious problems are uncommon. Gallbladder problems were about twice as common as on placebo (2.6% vs 1.2% with semaglutide). Pancreatitis occurred in about 0.2% of people. Sudden vision loss from NAION is a very rare side effect of semaglutide. Thyroid tumours seen in rodents haven’t been shown to occur in humans.

Gallbladder

• Semaglutide (STEP 1): gallbladder problems 2.6% vs 1.2% on placebo; gallstones 1.8% vs 0.6%.
• Tirzepatide: gallstones 1.1% vs 1.0%; gallbladder inflammation 0.7% vs 0.2%.
• Warning signs: pain under the right ribs, fever, yellow skin or eyes. See gallstones.

Pancreatitis

• Semaglutide: 0.2% vs 0% in STEP 1 (3 people). Across the US trials, 0.2 cases per 100 patient-years vs less than 0.1 on placebo.
• Tirzepatide: 0.2% vs 0.2% on placebo.
• Rare serious or fatal cases have been reported. Severe tummy pain that won’t settle, sometimes going through to the back, needs urgent help.

Sudden vision loss (NAION)

• In June 2025 the European Medicines Agency concluded that NAION (sudden damage to the optic nerve from poor blood flow) is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people.
• In people with type 2 diabetes, the risk was about twice that of non-users: roughly one extra case per 10,000 years of treatment.
• Sudden loss of vision or rapidly worsening eyesight needs urgent assessment.

Thyroid C-cell warning

• The US labels carry a boxed warning because semaglutide caused thyroid C-cell tumours in rodents. Whether it does in humans is unknown.
• Not for people with a personal or family history of medullary thyroid cancer or MEN 2.
• Tell your doctor about a new lump in your neck.

Mood

• In December 2025 the TGA added a warning about suicidal thoughts and behaviour to the whole class, while finding insufficient evidence that the medicines cause them.
• A UK MHRA review found the data don’t support a causal link. Tell your doctor about new or worsening low mood.

Other things to know

• Severe vomiting or diarrhoea can cause dehydration and kidney problems.
• Food can stay in the stomach under anaesthetic. See before surgery or anaesthesia.

Get urgent help (000 in Australia, or your local emergency number) for severe tummy pain that won’t settle, with or without vomiting, or swelling of the face or throat. See a doctor the same day if you can’t keep fluids down, have pain under the right ribs with fever or yellow skin, or notice sudden changes in your vision.

If you’re having thoughts of suicide or self-harm, call Lifeline on 13 11 14 (Australia, 24/7), your local crisis line, or 000 in an emergency.

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Evidence and more information

• Wilding et al, NEJM 2021: STEP 1, semaglutide 2.4 mg for weight management (weight loss, side-effect and gallbladder rates)
• US FDA prescribing information for Wegovy (semaglutide), February 2026: side-effect table, warnings
• US prescribing information for Zepbound (tirzepatide): side-effect table, gallbladder and pancreatitis rates
• European Medicines Agency, June 2025: NAION is a very rare side effect of semaglutide
• Healthed, December 2025: TGA adds suicidal ideation and behaviour warnings to GLP-1 medicines
• UK MHRA: GLP-1 medicines for weight loss and diabetes, what you need to know (updated February 2026)

Updated 8 November 2026. General education, not personal medical advice, and not a recommendation for any medicine. Whether a medicine suits you depends on your health and other medicines, so talk to your doctor or pharmacist.

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