Drug manufacturer Pfizer has entered into a definitive agreement to acquire Biohaven Pharmaceuticals, a maker of migraine treatments, for $11.6 billion, the former said this week.

Pfizer will also make payments at closing to settle Biohaven’s third party debt and for the redemption of all outstanding shares of Biohaven’s redeemable preferred stock.

The boards of directors of both Biohaven and Pfizer have unanimously approved the transaction.