Shares of Bristol-Myers Squibb fell 7% Monday after the pharmaceutical giant announced that the proposed acquisition of Celgene will now close later than originally expected and will involve a divestiture of Celgene's psoriasis drug.

In a Securities and Exchange Commission filing, the company said it now expects to close the planned $74 billion deal by the end of 2019 or beginning of 2020. It had originally expected to close the acquisition by the third quarter.

Celgene's stock also dropped 5%.

Bristol-Myers Squibb said that the divestiture of the drug Otezla would be used to help the company decrease financial leverage after the merger. Otezla generated about $1.6 billion in revenue last fiscal year for Celgene, according to a securities filing.

Bristol-Myers Squibb announced the acquisition in January but has not yet received approval from the Federal Trade Commission.

"Bristol-Myers Squibb is committed to working with regulatory authorities around the world on the proposed combination with Celgene. The company is focused on realizing the promise of the transaction, and is continuing to work to complete the transaction on a timely basis," the company said in a securities filing.

Shareholders of both companies had previously approved the deal.