Japan reissues GLP 1 appropriate use notice with a ketosis warning for slimming use

Japan's health ministry has recirculated its rules on GLP 1 drugs with a new ketosis warning attached. In a notice dated October 14 and sent to prefectures and large cities, four ministry divisions said they had received adverse reaction reports of ketosis related events in people who used GLP 1 or GIP/GLP 1 drugs for cosmetic or slimming purposes, though a causal link is unknown. The notice forwards a statement from the Japan Society for the Study of Obesity and repeats a June notice on appropriate use, advertising and side effect reporting.

What the October notice says

The notice is dated October 14, 2026 and carries the names of four division chiefs at the Ministry of Health, Labour and Welfare, including the pharmaceutical safety division. It is addressed to the health departments of prefectures, cities that run public health centres and Tokyo's special wards, and asks them to pass the message on to hospitals, clinics and pharmacies. It covers GLP 1 receptor agonists and GIP/GLP 1 receptor agonists approved in Japan for type 2 diabetes or for obesity disease. The ministry wrote that it has received reports of ketosis related adverse reactions where the drugs were used outside those approved uses, mainly for cosmetic or slimming purposes. It stated that the causal relationship with the drugs is unknown.

The trigger was a statement on safe weight loss that the Japan Society for the Study of Obesity released on October 3, 2026, which the ministry attached to its October 14 notice. The notice itself adds no new legal rule. It asks local authorities to make sure medical institutions understand both the society's statement and the earlier June notice. Japan's drug regulator, the PMDA, posted the documents on its safety notices page, according to the pharmacy trade publisher Yakubunsha. The ketosis warning therefore reaches doctors and pharmacists through the normal regulatory channel rather than through a label change. No product label has been changed so far, and the notice does not restrict any approved use for diabetes or obesity.

The ketosis warning in the obesity society statement

Ketosis is a state in which the body breaks down large amounts of fat and ketone bodies build up, often during severe food or carbohydrate restriction. When it progresses and the blood turns acidic, it becomes ketoacidosis, which can be dangerous. According to the society's statement as transcribed by Yakubunsha, the obesity society urged people to avoid combining these drugs with extreme dieting or strict carbohydrate cutting. The statement said cases leading to emergency transport or hospital admission have been reported in Japan and abroad. It linked the events to drug use combined with excessive food restriction or rapid weight loss, and said heavy drinking or use with SGLT2 inhibitors, a class of diabetes drugs, may raise the risk further.

The statement said cases leading to emergency transport or hospital admission have been reported in Japan and abroad.

The statement lists warning signs, Yakubunsha reported: a change in breath odour that smells sweet or sour, nausea, vomiting or abdominal pain, being unable to eat or drink, marked fatigue, drowsiness or confusion, and fast, deep breathing. Several of these overlap with the ordinary stomach side effects of the drugs, which is why the society asked clinicians not to dismiss them as routine. Its advice, as reported, is to stop both the drug and the diet at once when such signs appear and to seek medical care quickly. The society framed the ketosis warning as a call for safe weight loss and said it does not endorse weight loss with drugs outside their approved uses. People treated for diabetes or obesity are advised not to stop on their own but to speak to their doctor.

The June notice on appropriate use and advertising

The notice being recirculated dates from June 16, 2026. In it, the ministry said some medical institutions were using these drugs for cosmetic or slimming purposes outside type 2 diabetes and obesity treatment. It warned that safety and efficacy outside the approved indications and dosing have not been confirmed, and that serious side effects listed on the labels, such as low blood sugar and acute pancreatitis, can occur in off-label use too. Doctors were asked to explain the risks to users and to be ready to treat side effects promptly. The June notice also asked clinics and pharmacies to protect supply for patients who truly need the drugs. At that time, the ministry said, every product was shipping normally.

On advertising, the June notice reminded clinics that ads for self paid treatment using unapproved or off-label medicines are banned in principle under Japan's medical advertising rules. Websites are an exception, but only if they give a contact point and explain the usual treatment, its cost, risks and side effects. False or exaggerated claims remain banned even then. On safety reporting, it asked doctors and pharmacists to file adverse reaction reports under the Pharmaceuticals and Medical Devices Act and, when off-label use is clear, to write "off-label use (cosmetic purpose)" in the reason for use field. That tagging should make cases from slimming use easier to separate in Japan's safety data.

Approved obesity use and the wider regulatory picture

The June notice quoted the approved conditions to show how narrow the obesity indication is. For semaglutide as an obesity drug, the label limits use to people with high blood pressure, abnormal blood lipids or type 2 diabetes whose diet and exercise have not worked, and who either have a body mass index of 35 or more, or a body mass index of 27 or more with at least two obesity related health problems. People using the drugs only to look slimmer fall outside that group. The obesity society statement named several products as examples, including Wegovy, Ozempic, Rybelsus and Trulicity among GLP 1 drugs and Mounjaro and Zepbound among GIP/GLP 1 drugs, Yakubunsha reported.

Japan's step fits a pattern of regulators tightening their watch on these peptides as use spreads beyond approved patients. In Europe, the safety committee added a rare eye condition to semaglutide warnings after a review of reports. In the United States, the concern has centred on compounded copies, including a recall of compounded tirzepatide over sterility doubts. Japan's notice targets a different gap: approved, genuine products prescribed to people who do not meet the approved criteria. The ministry has not said how many ketosis reports it received or how severe they were, so the size of the problem is not yet public.

Conclusion

Japan has not changed any label, but the ketosis warning now travels with the ministry's appropriate use rules to every clinic and pharmacy. The message is narrow and practical: these drugs are approved for diabetes and obesity disease, slimming use is off label, and combining them with extreme dieting can tip some people into ketosis. The ministry says the causal link is unknown and has not published case numbers. Readers should treat the warning as a signal under watch, as set out in our editorial standards.