Infarmed Receives About One Suspected Side Effect Report a Day for GLP-1 Weight Loss and Diabetes Drugs
Portugal's medicines authority logged 695 suspected adverse reaction reports for GLP-1 drugs such as Mounjaro and Ozempic between January 2024 and September 2026. Nausea and vomiting lead the list; here is how to report a reaction.
Infarmed (the National Authority of Medicines and Health Products) has received 695 reports of suspected adverse reactions to GLP-1 receptor agonists, the class of diabetes medicines now widely used for weight loss, between 1 January 2024 and 21 September 2026. Infarmed gave the figures, from the SNF (National Pharmacovigilance System), to the Lusa news agency, as reported by RTP on 15 October.
The reports cover four active substances. There were 61 in 2024, 368 in 2025 and 266 up to 21 September this year: roughly one a day in each of the last two years.
Mounjaro accounts for most reports
Tirzepatide, the active substance in Mounjaro, which went on sale in Portugal in November 2024, accounts for most of them: 6 in 2024, 295 in 2025 and 186 so far in 2026. Semaglutide (Ozempic and Rybelsus) drew 12, 46 and 54 reports over the same periods; dulaglutide (Trulicity) 12, 21 and 21; and liraglutide (Victoza and Saxenda) 31, 6 and 5.
Use has grown sharply. Infarmed estimates that 10,689 packs of tirzepatide reached community pharmacies in mainland Portugal in 2024, 434,768 in 2025 and 395,369 in the first half of 2026. For semaglutide the estimates are 399,420, 626,142 and 485,424. Infarmed says these are extrapolated from a sample.
Measured against packs sold, Infarmed says the reporting rate has stayed broadly stable. For tirzepatide it was 0.56 reports per 1,000 packs in 2024, 0.68 in 2025 and 0.32 in the first half of 2026; for semaglutide 0.03, 0.07 and 0.06.
Nausea and vomiting lead the list
Nausea was the most commonly reported reaction (98 reports), followed by vomiting (68), diarrhoea (61) and constipation (41). Injection-site reactions (29), dizziness (27), headache (21) and hair loss (19) followed. Among the cases classed as serious were 26 of the 68 vomiting reports, 15 of the 61 diarrhoea reports, 13 of the 98 nausea reports and 5 of the 14 abdominal pain reports.
Since January 2024 Infarmed has also identified 19 cases with terms linked to pancreatitis, 17 involving liver or bile duct disorders and 6 involving kidney or urinary disorders. Infarmed stresses that these counts do not represent the share of users who suffered serious reactions, and one case can include several reactions. Spontaneous reports cannot on their own prove that a medicine caused a reaction; they are pooled at European level to detect safety signals.
One such signal has already led to a change. In June 2025 the European Medicines Agency's safety committee concluded that NAION, an eye condition that can cause loss of vision, is a very rare side effect of semaglutide (up to 1 in 10,000 people). Anyone noticing sudden loss of vision should contact their doctor without delay.
Supply has been a separate concern. In a July 2024 circular, Infarmed said off-label use for weight loss had significantly worsened shortages of Ozempic, Trulicity and Victoza and noted reports of counterfeits. It warned that these medicines can only be bought in pharmacies with a prescription.
How to report a reaction
Patients can report a suspected side effect themselves, without going through a third party, on Infarmed's Portal RAM (Portuguese only). Infarmed asks for, where possible, the patient's initials, age and sex; a description of the reaction; the medicine's brand name, active substance, dose and batch number (printed on the pack); any other medicines taken at the same time; and other illnesses. If you have trouble submitting, Infarmed's medicines information centre answers at [email protected], on +351 217 987 373 or on the free line 800 222 444. If you are worried about a reaction, speak to your doctor or pharmacist.
