Mounjaro 2.5 mg and 5 mg products (Photo provided by Korea Lilly)
SEOUL, Dec. 10 (Korea Bizwire) — At least 35 cases of adverse reactions, including several categorized as “serious,” have been reported in South Korea within a month of the launch of Mounjaro, Eli Lilly’s new obesity and diabetes treatment, according to data released Wednesday.
The figures were submitted to Rep. Seo Mi-hwa of the Democratic Party by the Korea Institute of Drug Safety & Risk Management, an agency under the Ministry of Food and Drug Safety. The reports cover August and September, immediately following the drug’s domestic introduction.
Among the 35 cases, five involved serious reactions requiring medical attention, including four instances of severe diarrhea and one case of hypoglycemic shock. Under South Korea’s drug safety rules, a “serious” adverse event is defined as a case involving death, life-threatening conditions, hospitalization or prolonged hospitalization, significant disability, or other medically significant situations requiring intervention.
Other reported side effects included muscle pain (six cases), injection-site bleeding (four), accidental underdosing (four), injection-site pain (three), upper abdominal pain (three), indigestion (three), headache (two), nausea (two) and constipation (two). One report cited injection-site redness.
Fifteen of the reported cases occurred in women and four in men. Age information was incomplete, with only seven cases involving adults between 19 and 65.
Mounjaro, a once-weekly injectable therapy, has rapidly gained traction in South Korea alongside Novo Nordisk’s Wegovy amid surging interest in new-generation obesity medications. The drug simultaneously activates GLP-1 and GIP hormone receptors to improve insulin secretion, reduce glucagon levels, delay gastric emptying and suppress appetite—leading to significant weight reduction.
Its sudden popularity has stoked concerns among health officials and clinicians about misuse, mounting demand and insufficient awareness of appropriate prescribing methods. Lawmakers have urged regulators to strengthen online advertising oversight and closely analyze safety reports.
The Korea Institute of Drug Safety stressed that adverse event notifications do not automatically establish causation between the drug and the reported outcomes, noting that reports may include cases where the drug is unlikely to be the cause.
Eli Lilly Korea echoed the position, saying the reported cases “do not necessarily indicate a causal link” to Mounjaro and that the company has complied with all reporting obligations since the drug’s launch. It pledged continued cooperation with government authorities and medical societies to ensure safe and appropriate use in Korea.
Lina Jang (linajang@koreabizwire.com)
