Osaka’s legal system has taken a significant step in addressing the illicit distribution of weight-loss medications after police referred three individuals to prosecutors for allegedly selling Mounjaro, a drug not approved for weight loss in Japan. The case underscores growing concerns over the black-market trade of prescription medications, particularly those repurposed for off-label use without regulatory oversight. As Japan’s third-largest city and a financial hub, Osaka’s response to this issue carries broader implications for public health and pharmaceutical enforcement across the country.
The three suspects, whose identities have not been publicly disclosed by authorities, are accused of violating Japan’s Pharmaceuticals and Medical Devices Act, which strictly regulates the sale and distribution of prescription drugs. Investigators reportedly confirmed that the individuals admitted to selling Mounjaro—a brand-name version of tirzepatide, a glucagon-like peptide-1 (GLP-1) receptor agonist originally approved for type 2 diabetes—without proper medical authorization. The drug has gained global attention for its efficacy in weight management, but its use for this purpose remains unapproved in Japan, where regulatory agencies like the Pharmaceuticals and Medical Devices Agency (PMDA) have not sanctioned it for non-diabetic indications.
This development follows a pattern of increased scrutiny on off-label drug use in Japan, where demand for weight-loss medications has surged amid rising obesity rates. According to the Ministry of Health, Labour and Welfare (MHLW), obesity-related illnesses now account for nearly 30% of all preventable health conditions in the country, driving a shadow market for unapproved treatments. While Mounjaro’s manufacturer, Eli Lilly and Company, has not commented publicly on the Osaka case, the company has faced regulatory challenges in Japan over its marketing practices for diabetes medications in other regions.
What Is Mounjaro, and Why Is Its Off-Label Use a Concern?
Mounjaro, developed by Eli Lilly, is a once-weekly injectable medication containing tirzepatide, a dual agonist that targets both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptors. While approved in the U.S. And EU for type 2 diabetes, its use for weight loss has been promoted through clinical trials showing significant reductions in body weight—sparking off-label demand. In Japan, however, the PMDA has not approved tirzepatide for weight management, citing insufficient domestic clinical data to support its safety and efficacy outside diabetes treatment.
The off-label use of Mounjaro poses multiple risks:
- Health hazards: Unsupervised use may lead to severe side effects, including pancreatitis, gallbladder issues, and thyroid tumors, as warned by the U.S. Food and Drug Administration (FDA) in its risk management plan.
- Regulatory gaps: Japan’s pharmaceutical laws prohibit the sale of unapproved drugs, but enforcement in underground markets remains challenging.
- Economic exploitation: Illicit sales often involve inflated prices, with Mounjaro reportedly selling for up to 10 times its approved cost in black markets.
For context, Japan’s obesity rate has risen to 4.3% of the population classified as severely obese (BMI ≥35) as of 2024, per MHLW data released last year. This backdrop fuels demand for unapproved solutions, despite warnings from health authorities.
How Japan’s Pharmaceutical Laws Address Unauthorized Sales
The Pharmaceuticals and Medical Devices Act (Act No. 136 of 1948) governs the manufacture, distribution, and sale of drugs in Japan. Key provisions relevant to this case include:
- Article 66: Prohibits the sale of drugs without proper approval or authorization.
- Article 78: Criminalizes the distribution of unapproved medications, punishable by up to 10 years in prison or fines.
- Article 80: Requires pharmacies and medical institutions to maintain records of drug distribution.
In practice, enforcement relies on cooperation between local police, the PMDA, and the National Police Agency (NPA). While Osaka’s move to prosecute the three individuals signals a crackdown, challenges persist in tracing illicit supply chains, particularly when drugs are smuggled from countries where Mounjaro is approved for weight loss.
Broader Implications for Public Health and Regulatory Enforcement
The Osaka case aligns with a broader crackdown on pharmaceutical violations in Japan. In 2025, authorities dismantled a large-scale online drug trafficking network linked to unapproved weight-loss and performance-enhancing substances, resulting in 12 arrests. Experts warn that the rise of telemedicine and cross-border e-commerce has exacerbated the problem, making it easier for consumers to access unregulated treatments.
For stakeholders, the implications are clear:
- Patients: Risk of counterfeit or substandard products, with no recourse for adverse effects.
- Healthcare providers: Ethical dilemmas over prescribing off-label drugs amid patient demand.
- Regulators: Pressure to balance innovation with public safety, particularly as global pharmaceutical trends shift toward repurposing existing drugs.
- Manufacturers: Reputational risks if associated with unapproved distribution channels.
Eli Lilly, for instance, has faced scrutiny in other markets over its marketing practices. In 2023, the company settled a lawsuit in the U.S. Over alleged off-label promotions of Mounjaro’s weight-loss benefits, paying $1.3 billion to resolve claims under the False Claims Act. While Japan’s legal framework differs, the case highlights the global tension between commercial incentives and regulatory compliance.
What Happens Next in the Osaka Case?
Prosecutors in Osaka will now review the evidence to determine whether to file formal charges. If convicted, the three individuals could face penalties under Article 78 of the Pharmaceuticals and Medical Devices Act, which carries potential imprisonment or fines. However, the outcome will depend on factors such as:
- The volume and value of Mounjaro distributed.
- Whether the sales involved organized criminal networks.
- Cooperation with authorities during investigations.
For updates, residents can monitor official statements from the Osaka Prefectural Police or the PMDA. Meanwhile, the case may prompt broader discussions on:
- Expanding access to approved weight-management therapies in Japan.
- Strengthening cross-border pharmaceutical enforcement.
- Public awareness campaigns on the dangers of unapproved medications.
Key Takeaways
- Regulatory gap: Mounjaro’s off-label use in Japan reflects a mismatch between global demand and domestic approvals.
- Legal risks: Sellers and buyers of unapproved drugs face criminal penalties under Japan’s strict pharmaceutical laws.
- Public health threat: Unsupervised use of GLP-1 agonists carries serious health risks, including organ damage.
- Enforcement challenges: Illicit markets thrive due to telemedicine and international smuggling routes.
- Broader context: The case is part of a larger trend of pharmaceutical violations in Japan, requiring coordinated regulatory responses.
As the Osaka prosecution proceeds, the story serves as a reminder of the complexities surrounding pharmaceutical innovation, regulatory oversight, and public health. For readers seeking further information, the MHLW’s drug safety portal and the PMDA’s approval database offer authoritative resources on approved medications in Japan.
We welcome your insights on this issue. Have you or someone you know been affected by the unapproved sale of weight-loss medications? Share your experiences in the comments below, and stay tuned for further updates as this story develops.