Japan obesity society warns against weight-loss use of Mounjaro and Wegovy
In short
Japan’s Obesity Society issued a statement warning that using Mounjaro, Wegovy and other GLP-1 drugs for dieting — especially alongside severe food restriction — can cause ketone bodies to build up, leading to vomiting, abdominal pain and, in severe cases, ketoacidosis. About 950 adverse-reaction reports for Mounjaro reached Japan’s PMDA from 2023 through Sept. 22, of which 35 involved off-label use for diet or cosmetic purposes. In Japan the drug can be obtained through uninsured “free treatment,” and its price is seen as relatively low, which outlets linked to demand for buying it abroad and the Korean nickname “sushijaro.”
Why it matters
The warning concerns GLP-1 weight-loss drugs that are in demand across borders, including from South Korea, where buying the drug in Japan has become common enough to earn a nickname. The reports say off-label cosmetic use in Japan may leave patients outside the country’s side-effect compensation system and that drugs bought through social media or secondhand trading may be counterfeit. That makes the practical risks of self-directed use, rather than only the drug’s effects, the core of the story for readers considering the same route.
Key facts
- Japan’s Obesity Society issued a statement warning about the use of Mounjaro, Wegovy and other GLP-1 drugs for weight loss, saying rapid loss can cause ketone bodies to accumulate and lead to vomiting, abdominal pain and fatigue. [ 1 , 2 ]
- The society said ketoacidosis — excess ketone bodies acidifying the blood — can occur, with severe cases bringing dehydration and impaired consciousness and possibly requiring emergency treatment. [ 1 , 2 ]
- Japan’s Pharmaceuticals and Medical Devices Agency (PMDA) received about 950 reports of adverse reactions to Mounjaro from 2023 through Sept. 22, of which 35 involved use for diet or cosmetic purposes outside the approved indication. [ 1 , 2 ]
- Mounjaro is a tirzepatide injection approved in Japan as a type 2 diabetes treatment, while the same ingredient is approved for obesity under the name Zepbound. [ 2 ]
- In Japan the drug requires a prescription in principle but can be obtained through uninsured “free treatment” for cosmetic or weight-loss purposes, and its price as a type 2 diabetes treatment is government-managed and seen as relatively low. [ 1 , 2 ]
- Japan’s health ministry warns that buying medicines through social media or online secondhand trading is illegal and that such products may be counterfeit or degraded, and says compensation is unlikely under the side-effect relief system for unapproved uses. [ 2 ]
- Demand for buying Mounjaro in Japan, including through purchasing agents, has grown, and in South Korea the term “sushijaro” has appeared for the practice. [ 1 , 2 ]
Confirmed by several sources
- Japan’s Obesity Society issued a statement warning about the use of Mounjaro and other GLP-1 drugs for diet or cosmetic purposes. [ 1 , 2 , 3 ]
- The warnings say misuse can cause vomiting and abdominal pain. [ 1 , 2 , 3 ]
- PMDA received about 950 adverse-reaction reports on Mounjaro from 2023 through Sept. 22, including 35 for off-label diet or cosmetic use. [ 1 , 2 ]
- Mounjaro requires a prescription in principle but is obtainable in Japan through uninsured “free treatment,” and its price there is seen as relatively low. [ 1 , 2 ]
Still unclear
- What prompted the obesity society’s statement at this time Both detailed reports say only that cases have recently been reported, without identifying a specific case or cluster.
- When and where the statement was issued The reports describe it only as a recent statement and give no date or venue.
- Whether Mounjaro is in fact cheaper in Japan than in South Korea The reports describe a widespread perception of a lower Japanese price rather than citing specific prices in either country.
- How many clinics in Japan prescribe the drug off-label and in what volumes Seoul Economic Daily says such clinics exist and that the drug is available through uninsured care, but no figures are given.
- What the Newsis report contained beyond its headline Its attached article text covers unrelated remarks by a political figure, so only its headline on the Mounjaro warning could be used.
What local media are saying
Timeline, local time
- Asia Economy publishes a report on the Japanese obesity society’s warning and the PMDA figures. [ 1 ]
- Seoul Economic Daily publishes a fuller report adding the health ministry’s warnings on online sales and side-effect compensation. [ 2 ]
- Newsis publishes a report with the same warning headline. [ 3 ]