Italy, 1836. Nemorino, a young villager, is unhappily in love with the beautiful farm owner Adina, who he thinks is beyond his reach. Adina tells the gathered peasants about the book she is reading—the story of how Tristan won the heart of Iseult by drinking a magic love potion. A regiment of soldiers arrives, led by the pompous Sergeant Belcore, who immediately introduces himself to Adina and asks her to marry him.
Adina declares that she is in no hurry to make up her mind but promises to think over the offer. Left alone with Nemorino, Adina tells him that his time would be better spent in town, looking after his sick uncle, than hoping to win her love. She suggests that he do as she does and change affections every single day. Nemorino reminds her that one can never forget one’s first love.
Dr. Dulcamara, a traveling purveyor of patent medicines, arrives in the village advertising a potion capable of curing anything. Nemorino shyly asks him if he sells the elixir of love described in Adina’s book. Dulcamara claims he does, slyly proffering a bottle of simple Bordeaux. He explains that Nemorino will have to wait until the next day—when the doctor will be gone—to see the results Though it costs him his last ducat, Nemorino buys and immediately drinks it.. Nemorino begins to feel the effect of the “potion” and, convinced he will be irresistible to Adina the next day, feigns cheerful indifference towards her. Surprised and hurt, Adina flirts with Belcore. When orders arrive for the sergeant to return immediately to his garrison, Adina agrees to marry him at once. The shocked Nemorino begs her to wait one more day, but she dismisses him and invites the entire village to her wedding. Nemorino desperately calls for the doctor’s help.