Serotonin is a novel by Michel Houellebecq, first published in 2019. The book tells the story of Florent-Claude Labrouste, a middle-aged agronomist who struggles with depression and the search for the meaning of life. The main character embarks on a journey to find lost love and happiness. The novel addresses the problems of contemporary society, including loneliness, the lack of love, and the quest for life's purpose. Houellebecq's style is characterized by depth and irony, which makes the book particularly appealing.