Allergan has confirmed it is in talks with Pfizer about a merger.
In a statement on Thursday, the Botox-maker said it had been approached and was in "preliminary friendly discussions".
A deal has not been finalized.
This is Pfizer's second recent attempt to take over a big rival, following the failed bid for Anglo-Swedish group AstraZeneca, according to Reuters.
Reports on Wednesday indicated that both companies were in discussions to create what would be the world's largest healthcare company with a combined market cap of around $330 billion.
Trading in shares of both companies was halted just before the announcement.
Here's the full statement:
Allergan plc today confirmed that it has been approached by Pfizer Inc. and is in preliminary friendly discussions regarding a potential business combination transaction. Allergan stated that no agreement has been reached and there can be no certainty that these discussions will lead to a transaction, or as to the terms on which a transaction, if any, might be agreed. The company will not comment on speculation regarding the terms of a potential transaction.
Under any potential scenario with Pfizer, Allergan remains strongly committed to complete the proposed divestment of its global generics business to Teva Pharmaceutical Industries Ltd and expects the generics divestiture transaction to close in the first quarter of 2016.
A further announcement will be made when appropriate.