The European Commission has approved US drugmaker AbbVie's planned $63 billion acquisition of Dublin headquartered Botox-maker Allergan, subject to conditions.

The Commission, which oversees competition policy in the European Union, said its approval was conditional on the divestment of a product under development by Allergan to treat inflammatory bowel diseases.

"Our decision makes sure that the merger between AbbVie and Allergan will not disrupt the development of a promising innovative treatment for these diseases," Margrethe Vestager, commissioner in charge of competition, said in a statement.

The Commission had found that Allergan's brazikumab was likely to compete with AbbVie's risankizumab, but the merger would have led to research into brazikumab to be halted, "preventing a promising drug from reaching the market".

To address the commission's concerns AbbVie has agreed to sell brazikumab to an investor that would continue its development.

AbbVie announced its plans to acquire Allergan in June to give it control of lucrative wrinkle treatment Botox and buying time to seek new growth before its blockbuster arthritis treatment loses US patent protection.

Allergan has four facilities here, employing around 2,000 staff.

Its Westport campus is the largest and most complex in the company's global network. 

It includes a pharmaceuticals facility, two biologics plants and an ocular implant facility and is also responsible for the global supply of Botox. 

Chicago headquartered AbbVie has five sites in Ireland, including three manufacturing facilities in Sligo and Cork, and two offices in Dublin.

More than 700 people are employed across the various locations.