Weight-Loss Drug Adverse-Event Reports Reach 1,780 in Korea

Reports of adverse events following the use of the injectable weight-loss drugs Wegovy and Mounjaro have reached 1,780 in South Korea, according to government data released Friday, highlighting the need for closer monitoring as demand for obesity treatments grows rapidly.

The figures submitted to ruling Democratic Party lawmaker Kwon Chil-seung showed 944 reports involving Wegovy from its domestic launch in October 2024 through March 2026. The annual total rose from 49 in 2024 to 672 in 2025, with another 223 reports recorded during the first three months of this year.

Mounjaro, which entered the Korean market in August 2025, was linked to 836 reports over the same reporting period. Of those, 345 were filed last year and 491 in the first quarter of 2026. When 518 reports involving Saxenda between 2024 and March this year are included, the combined total for the three injectable obesity medicines reaches 2,298.

Frequently reported symptoms included vomiting, diarrhea, pain at the injection site, headaches and indigestion. Health authorities emphasized that an adverse-event report documents a health problem observed after a medicine was taken and does not on its own establish that the drug caused the problem. Kwon likewise cautioned against treating the figures as proof of causation, while calling for stronger oversight as use expands.

Prescription data underline the pace of growth. Mounjaro was prescribed about 1.84 million times through July 2026, compared with 394,365 prescriptions during the final five months of 2025. Wegovy recorded 482,071 prescriptions through July after 828,209 last year. The totals count prescription records rather than individual patients, so they should not be interpreted as the number of people receiving treatment.

The medications work in different ways. Wegovy contains semaglutide, while Mounjaro contains tirzepatide, which acts on both GIP and GLP-1 receptors. Saxenda contains liraglutide. All three are prescription injections designed to reduce appetite.

Rapidly rising demand has also increased concern about products acquired outside authorized distribution channels. Customs authorities intercepted 5,030 attempts to bring obesity drugs into Korea illegally through August, more than four times the 1,189 cases detected during all of 2025.

Tests of nine suspected counterfeit Mounjaro products shipped from India found inconsistent tirzepatide levels and unidentified impurities in some samples. Officials also said the products were transported without the required cold chain, adding a storage and safety risk beyond uncertainty about their contents. The findings reinforce warnings that patients should obtain the treatments through licensed medical and pharmacy channels and use them under professional supervision.