📌 Key Takeaways
- On June 2, 2026, Osaka Prefectural Police filed charges against three individuals for illegal sales of Mounjaro (tirzepatide) on social media under Japan’s Pharmaceutical Affairs Act—the first such prosecution in Osaka. Tokyo’s Pharmaceutical Affairs Division also issued an unprecedented direct warning on X (formerly Twitter).
- Mounjaro is approved in Japan only for type 2 diabetes treatment. Weight loss use is off-label. The same active ingredient is available as Zepbound, approved for obesity treatment and launched in April 2025.
- “Effective” and “safe to use” are not the same. NERO outlines three critical risks—legal, quality, and medical—that consumers must understand before making decisions.
In 2019, “blood cleansing” therapy ignited controversy in Japan. An aesthetically-oriented treatment with weak medical evidence spread via social media and faced scrutiny for suspected false advertising.
More than six years later, in 2026, a strikingly similar structural problem has emerged—in a far more dangerous form. This time, it involves Mounjaro.
INDEX
What Happened: May–June 2026 Timeline
📅 May–June 2026: Administrative and Legal Actions on Mounjaro
Tokyo Metropolitan Government’s Pharmaceutical Affairs Division issued a direct warning via official X account to users selling Mounjaro: “Selling Mounjaro, a pharmaceutical product, without authorization violates the Pharmaceutical Affairs Act. Cease sales immediately.” (Tokyo Pharmaceutical Affairs Division, Official X, May 28, 2026)
Osaka Prefectural Police filed charges against three individuals (ages 22–35, residents of Osaka and Nara prefectures) for unauthorized sale and storage of Mounjaro under the Pharmaceutical Affairs Act. This marks the first such prosecution in Osaka. All suspects admitted to the charges. (Asahi Shimbun, Sankei Shimbun, June 2, 2026)
What Is Mounjaro? Understanding the Basics
The generic name is tirzepatide. Developed by U.S. pharmaceutical giant Eli Lilly, it is an injectable drug that acts as a dual incretin agonist, targeting both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors simultaneously. In Japan, it was approved by the Ministry of Health, Labour and Welfare in September 2022 exclusively for type 2 diabetes treatment.
Due to its appetite-suppressing effects leading to weight loss, demand for off-label weight loss use surged. Notably, Zepbound, an obesity treatment drug containing the same active ingredient (tirzepatide), was launched in Japan in April 2025, providing an approved treatment option for patients medically diagnosed with obesity.
Three Critical Risks: “Effective” ≠ “Safe to Use”
The weight loss efficacy of Mounjaro is well-documented in multiple large-scale clinical trials. The SURMOUNT-1 trial demonstrated average weight loss of 15–20% over 68 weeks in obese patients without diabetes (NEJM 2022).
However, “effective drug” and “safe to obtain and use” are entirely separate issues.
⚠️ Risk ① Obtaining via Social Media Resale or Personal Import Carries Severe Risks
Mounjaro is a prescription-only drug. Selling or transferring it without a physician’s prescription violates Japan’s Pharmaceutical Affairs Act. Purchasing from social media or flea market app resellers, or via overseas personal import (including import agency sites), poses serious problems. In the prosecuted cases, individuals resold medication prescribed for their own diabetes treatment. Even “sharing medication prescribed for personal use” constitutes a criminal offense under Articles 66 and 68 of the Pharmaceutical Affairs Act, subject to criminal penalties.
⚠️ Risk ② Counterfeit Products Have Contained Different Drugs—This Is Not Just an “Overseas Problem”
In February 2026, the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) issued an urgent alert regarding specific batches of Mounjaro KwikPen products. Counterfeit products were found to contain insulin instead of the intended active ingredient (tirzepatide), posing severe hypoglycemia risks from accidental administration. Both WHO and manufacturer Eli Lilly have issued warnings about counterfeit products.
Do not dismiss this as “a UK problem.” When purchasing from social media resellers or personal import agency sites, it is impossible to trace the distribution chain—overseas factories, intermediaries, cross-border shipping—or identify where counterfeits entered the supply. Visual identification is virtually impossible. Consider what lies behind “cheap prices.”
⚠️ Risk ③ Off-Label Use Excludes Adverse Reaction Relief Coverage; Rebound Risk Exists
Common adverse effects include gastrointestinal symptoms and gallbladder-related events (cholelithiasis, cholecystitis). Japan’s PMDA has issued warnings. Weight loss or aesthetic use is off-label; if serious adverse effects occur, patients cannot access Japan’s national adverse drug reaction relief system.
Equally critical is rebound risk. The SURMOUNT-4 trial found that after 36 weeks of treatment, discontinuation led to most participants regaining 25% or more of lost weight within one year (JAMA January 2024; Horn et al. JAMA Intern Med 2025).
Do not underestimate “only 25% regain.” The reality is “weight tends to return toward baseline levels after stopping the drug.” In other words, casual use may ultimately force a choice: continue paying for expensive out-of-pocket treatment indefinitely, or return to original weight. Have physicians explained the economic risk of paying tens of thousands of yen monthly for years?
“Off-Label Prescribing” Is Not Illegal—But Physicians Bear Heavy Responsibilities
Off-label prescribing of Mounjaro for weight loss at aesthetic or private-pay clinics is not immediately illegal under physician discretion. However, physicians must fulfill the following obligations:
Physicians’ duty to inform exists legally. However, in practice, Mounjaro is marketed as a “convenient weight loss injection,” and counseling often fails to adequately convey “off-label use status” or “exclusion from adverse reaction relief coverage.”
Informed consent becomes perfunctory, with prescriptions decided by a single phrase: “We have an effective weight loss injection.” This structural problem is the core issue. NERO has repeatedly highlighted this “information asymmetry” with ECM products and exosomes—the exact same structure now occurs with a more direct pharmaceutical intervention.
- Explicitly inform patients of “off-label use” and obtain consent
- Clearly state “exclusion from adverse drug reaction relief system”
- Explain that an approved obesity drug (Zepbound) exists before deciding on prescription
- Provide explanation including rebound risk and long-term treatment planning
Prescribing without these explanations under the guise of “weight loss injection” raises ethical and legal concerns.
This issue must not be reduced to “resellers are bad”—an individualized problem. Two structural issues exist.
First, information asymmetry where “effective drugs” are perceived as “safe to use.” Second, lack of informed consent where patients are prescribed without knowledge of off-label use or relief system exclusion.
This mirrors the exact structure NERO has repeatedly identified with ECM products and exosomes. Information about “cutting-edge effectiveness” circulates while risks fail to reach patients.
We are not calling Mounjaro a “bad drug.” Our consistent stance: “Patients have the right to know what they are being prescribed.”
Summary
- On June 2, 2026, three individuals were charged under the Pharmaceutical Affairs Act for unauthorized Mounjaro sales on social media (Osaka Prefectural Police). Tokyo’s Pharmaceutical Affairs Division also issued direct warnings via official X.
- Mounjaro is approved in Japan only for type 2 diabetes treatment. For obesity, Zepbound (same ingredient) launched in April 2025.
- Three critical risks: ① Social media resale/personal import involves complicity with illegal sales networks and counterfeit product risks ② Counterfeit products containing different drugs confirmed (UK MHRA warning) ③ Off-label use excludes adverse reaction relief coverage
- Off-label prescribing is not immediately illegal, but physicians must explain “off-label status, relief system exclusion, and rebound risk” to patients
Frequently Asked Questions
Sources
Asahi Shimbun “Mounjaro spread on social media as weight loss drug: Three charged for unauthorized sales” Yahoo! News Japan, June 2, 2026 / J-CAST “‘Cease sales immediately’: Tokyo Metropolitan Government Pharmaceutical Affairs Division issues warning on X regarding Mounjaro” May 29, 2026 / Tokyo Pharmaceutical Affairs Division (@tocho_yakumu) Official X, May 28, 2026 / UK MHRA “Falsified Mounjaro (tirzepatide) KwikPen alert” February 2026 / WHO Medical Product Alert (Falsified tirzepatide) / Eli Lilly “Open Letter Regarding Falsified Tirzepatide” / Japan PMDA “Tirzepatide (Mounjaro subcutaneous injection) package insert” / Jastreboff AM et al. “Tirzepatide Once Weekly for the Treatment of Obesity” NEJM 2022 / Garvey WT et al. “Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2)” Lancet 2023 / Aronne LJ et al. “Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial” JAMA January 2, 2024 (DOI:10.1001/jama.2023.24945) / Horn DB et al. “Cardiometabolic Parameter Change by Weight Regain on Tirzepatide Withdrawal in Adults With Obesity: A Post Hoc Analysis of the SURMOUNT-4 Trial” JAMA Intern Med November 24, 2025 (DOI:10.1001/jamainternmed.2025.6112)
