The agency has been appointed by Reckitt Benckiser following Reckitt's acquisition of the Boots Healthcare business. The task includes the Nurofen, Strepsils, E45, Optrex and Clearasil brands.
MindShare previously handled the account but Reckitt has consolidated the business into OMD, which handles planning and buying for its other brands.
Reckitt's £1.9 billion acquisition of Boots Healthcare International was approved at the end of January.
Creative duties for the brands remain with McCann Erickson. Reports had suggested the business would be split between Reckitt's roster agencies, JWT and Euro RSCG London.
Neil Duncan, the business director for Reckitt at OMD UK, said: "We are delighted to be extending our relationship with Reckitt Benckiser. They have an excellent track record in growing brands and we look forward to contributing to the development of their latest acquisitions."