 However, soon after the death of Hakim Ajmal Khan, Siddiqui left the post.In 1940, he joined Indian Council for Scientific and Industrial Research where he worked until 1951 when he migrated to Pakistan on the request of Prime Minister Liaquat Ali Khan.Siddiqui's first breakthrough in research came when he successfully isolated an antiarrhythmic agent in 1931 from the roots of Rauvolfia serpentina.