Although the Alfa Romeo team had proved to be competitive under the management of Enzo Ferrari, Varzi decided to join the Auto Union team, racing for them between 1935 and 1937. This move coincided with Varzi having serious personal problems, including an addiction to morphine and a difficult affair with Ilse Pietsch (Engel/Hubitsch/Feininger), the wife of a fellow driver Paul Pietsch. Quickly overshadowed by teammate Bernd Rosemeyer, his trips to the winners circle dropped to only four, but he did win his third Tripoli Grand Prix in his third different vehicle. By 1938 he had dropped out of sight and the advent of World War II ended racing in Europe. During the war, Varzi overcame his drug addiction and settled down with his new wife, Norma Colombo. At the end of the War, Varzi made a remarkable comeback at the age of 42. In 1946 he attempted to race a Maserati for the Indianapolis 500 but failed to qualify. In 1947, he won three minor Grand Prix races and traveled to Argentina to race in the Buenos Aires Grand Prix.