The Ugly Duckling (1959)

Henry Jeckle was always the outsider, a bungling and awkward buffoon, relegated to waiting for his invitation to participate in life that never arrived: until he discovers a medical formula developed by a dead uncle, which claimed to turn 'a man of timid disposition into a bold, fearless dragon'. Taking a draught of the elixir Henry is transformed into suave, sophisticated and highly desirable Teddy Hyde. Armed with his new persona, Teddy is ready to face the world; but is Henry ready for the consequences?
https://www.imdb.com/title/tt0174303/