The compound was protected by a patent which was assigned to the German pharmaceutical company Hoechst AG (since merged into Aventis) on 29 October 1991. The patent was scheduled to expire on 29 October 2008. On 11 September 2007, in an appeal by the Indian company Lupin Ltd., the United States Court of Appeals for the Federal Circuit reversed a district court trial verdict and found that Aventis's patent on ramipril was invalid for "obviousness", opening this drug to generic manufacturers.