Do remedies affect the efficiency defense? An optimal merger-control analysis

► We study the optimal mix remedies-efficiency defense in horizontal merger control. ► The efficiency defense pushes firms to enhance the merger's efficiency gains. ► The remedies improve the merger assessment. ► For very good information quality, the agency should optimally give up remedies. ► Using both instruments is optimal for an intermediate range of information quality. ► For poor information quality, the agency should prohibit the efficiency defense.