The deal is the largest-ever by a Japanese company and gives Takeda a lucrative portfolio of rare disease drugs.
The drug maker says the deal will further its goal of "building the leading biotechnology company focused on rare diseases."
The deal gives the acquisitive Irish company access to an experimental drug that competes with its own treatment for a rare disease.
The hue and cry over tax inversions is not stopping companies from proceeding with more mergers that take advantage of the tactic.
AbbVie's plans to pay less taxes by relocating to Britain after buying Shire touches a raw nerve in Washington.
