 Farquhar left the regiment at Gibraltar and spent 18 months travelling and studying medicine in France, working with Claude Nicolas le Cat in Rouen.In 1769, citing ill-health, Farquhar retired from the army and moved to London, opening an apothecary shop in Great Marlborough Street with his wife Anne Harvie, widow of a London doctor.Farquhar's practice gradually developed a steady clientele and he became a physician, awarded his MD from King's College, Aberdeen in 1796.