Kissei Pharmaceutical, which sells the autoimmune drug Tavneos in Japan, warned doctors on May 15 to stop prescribing the drug to new patients and to carefully reassess those currently taking it after 20 deaths were reported in Japan since the drug’s launch in June 2022 [1, 2]. Tavneos has been given to around 8,500 patients in Japan since its approval [1].

Tavneos, owned by Amgen following its $3.7 billion acquisition of ChemoCentryx in 2022, treats rare autoimmune diseases causing blood vessel inflammation known as ANCA-associated vasculitis [1, 2]. While 20 deaths have occurred in Japan, Amgen noted that some of these cannot be conclusively linked to the drug. It said there have been "no known deaths in the US linked to serious liver injury" among over 8,000 patients treated there with Tavneos [1].

The US Food and Drug Administration (FDA) has raised concerns about Tavneos, proposing to withdraw its approval due to issues including data tampering, false statements, and insufficient evidence of effectiveness [1, 2]. The FDA said, "There isn’t enough evidence showing that Tavneos is effective, and that its original drug application contained false statements" [2]. European regulators including the European Medicines Agency are also reviewing the drug based on data integrity concerns [1, 2].

Tavneos was first approved in the United States in 2021 and subsequently approved and launched in European countries and Japan in 2022 [1, 2]. Earlier this year in April 2026, Amgen maintained that the benefits of Tavneos still outweigh the risks [2].

Previously, the FDA had linked Tavneos to eight deaths, but specific earlier death counts before the 20 reported in Japan have not been confirmed across sources [1, 2]. The causal link between the drug and the deaths in Japan remains unclear; some cases show no direct connection to Tavneos [1, 2].

Kissei’s warning directs doctors to stop prescribing Tavneos to new patients and to assess those already on the medication "carefully" [2]. The company’s alert marks the latest development as regulators around the world review Tavneos’ safety and efficacy.

The next major regulatory step is pending FDA’s final decision on withdrawing Tavneos approval due to the outstanding safety and data concerns [1, 2].