Wegovy and Mounjaro Side Effects: What the FDA and EMA Say, and Korea’s Reported NAION Case

Information as of October 14, 2026.

GLP-1 weight-loss injections such as Wegovy (semaglutide) and Mounjaro (tirzepatide) are now widely used in South Korea. At the National Assembly’s annual audit of government agencies on October 13, the head of the Ministry of Food and Drug Safety (MFDS), Korea’s drug regulator, was questioned about a suspected case of vision damage after Wegovy use. This explainer sets out the side effects using the official US FDA prescribing labels (via DailyMed) and the European Medicines Agency (EMA), then covers what was said in Korea.

Common side effects

According to the FDA labels, the most common adverse reactions (reported in 5% or more of patients) include:

• Wegovy: nausea, diarrhoea, vomiting, constipation and abdominal pain, among others such as headache, fatigue, indigestion and dizziness. (Wegovy label)
• Mounjaro: nausea, diarrhoea, decreased appetite, vomiting, constipation, indigestion and abdominal pain. (Mounjaro label)

Both lists come from FDA labels, which are a single official source and have not been cross-checked elsewhere.

Label warnings

• Acute pancreatitis: both labels warn about it. Symptoms can include persistent or severe abdominal pain, sometimes spreading to the back. If pancreatitis is suspected, the labels say to stop the drug. Korean media have also reported pancreatitis cases after prescriptions. (Wegovy label, Mounjaro label, JoongAng Ilbo)
• Acute gallbladder disease (gallstones, inflammation of the gallbladder): on both labels.
• Thyroid C-cell tumours: a boxed warning based on rodent studies. It is unknown whether the drugs cause these tumours in humans.
• Other warnings: low blood sugar when used with insulin or sulfonylureas; acute kidney injury linked to dehydration; and a risk of aspiration under general anaesthesia or deep sedation.

JoongAng Ilbo reported data from Korea’s Health Insurance Review and Assessment Service (HIRA) on patients treated for pancreatitis after these prescriptions. We have not included the figures because they appear in that report only and we could not find an official page. Causation has not been established.

NAION: a very rare eye condition

NAION (non-arteritic anterior ischaemic optic neuropathy) is damage to the optic nerve from reduced blood flow, which can cause sudden loss of vision. In June 2025 the EMA’s safety committee (PRAC) concluded that NAION is a very rare side effect of semaglutide, meaning it may affect up to 1 in 10,000 people taking it. Studies in adults with type 2 diabetes suggest roughly a two-fold higher risk, or about one extra case per 10,000 person-years of treatment. The EMA advises patients with sudden vision loss or rapidly worsening eyesight to contact their doctor without delay, and to stop semaglutide if NAION is confirmed. (EMA, Electronic Times) The EMA review covers semaglutide (Wegovy, Ozempic, Rybelsus), not tirzepatide (Mounjaro).

The Korean case

At the October 13 audit, MFDS Minister Oh Yu-kyoung said one suspected NAION case after Wegovy use had been reported in Korea in December 2024. Lawmakers criticised the regulator for acting slowly. Reports differ on what happened next: Hankyoreh quoted her as saying the MFDS had applied on October 7 to add NAION to the approved product information, while Electronic Times quoted her as saying the change was completed on October 7. We could not find an official MFDS notice, so this is unconfirmed. (Hankyoreh, Electronic Times)

FAQ

What if the nausea doesn’t go away?
The labels warn that dehydration from nausea, vomiting or diarrhoea can lead to kidney injury. If symptoms persist, talk to your doctor.

What if my vision suddenly blurs?
The EMA says to contact your doctor without delay.

Does the Korean label differ from the US one?
These sources don’t give a full comparison. Check the MFDS-approved product information or ask a pharmacist.

This article summarises public US FDA and European Medicines Agency information and news reporting. It is not medical advice. Decisions about starting or stopping treatment, dosage and side effects must be made with a doctor, pharmacist or other medical professional. Written by the Haesul Global health desk with AI assistance.

Korean edition: 위고비·마운자로 부작용 체크리스트 (haesul.com)

Sources

• US FDA prescribing information via DailyMed (US National Library of Medicine), WEGOVY label (revised June 2026), https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b (2026년 10월 14일 확인)
• US FDA prescribing information via DailyMed, MOUNJARO label (revised August 2026), https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d2d7da5d-ad07-4228-955f-cf7e355c8cc0 (2026년 10월 14일 확인)
• European Medicines Agency, Jun 6, 2025 (revised Jun 13), “PRAC concludes eye condition NAION is a very rare side effect of semaglutide medicines Ozempic, Rybelsus and Wegovy”, https://www.ema.europa.eu/en/news/prac-concludes-eye-condition-naion-very-rare-side-effect-semaglutide-medicines-ozempic-rybelsus-wegovy (2026년 10월 14일 확인)
• Hankyoreh, Oct 13, 2026, “식약처장 ‘위고비 투약 뒤 시력 손상 의심 2024년에 1건 접수'” (MFDS chief: one suspected vision-damage case reported in 2024), https://www.hani.co.kr/arti/society/health/1282166.html (2026년 10월 14일 확인)
• Electronic Times (etnews), Oct 13, 2026, “[2026 국감] 식약처, 위고비 시력손상 부작용 대응 도마 위…국내 1건”, https://www.etnews.com/20261013000263 (2026년 10월 14일 확인)
• JoongAng Ilbo, Oct 13, 2026, report on pancreatitis treatment after Wegovy/Mounjaro prescriptions (figures not used), https://www.joongang.co.kr/article/25469361 (2026년 10월 14일 확인)