Scene 1: Adina's farm
The peasants are resting after work on Adina's farm. She is reading, watched by Nemorino, who loves her but is too shy to approach her. Adina tells everyone that she has been reading how Tristan, pining with love for Isolde, drank a love potion which caused her to fall in love with him.
Arriving to a drum roll at the head of his soldiers, Belcore gives Adina a bouquet and proposes marriage, confident that no girl can resist a soldier. She declines the offer, and the jealous Nemorino wishes he could approach her as confidently as Belcore. Adina offers wine to Belcore and his men.
Nemorino plucks up the courage to speak to Adina of his love, but she answers that she is capricious and wishes to remain free, advising him to go to the city and live with his rich, ailing uncle. He is unable to accept her advice to love lightly as she does.
Scene 2: The village square
Heralded by a trumpet, the quack Dr Dulcamara arrives, promising potions to cure all ills. Nemorino asks if he has Queen Isolde's elixir and Dulcamara, at first puzzled, recovers and pretends to have just the thing. He sells Nemorino a bottle of the elixir - actually wine - with instructions to drink it slowly. By the time Adina arrives, Nemorino is sufficiently drunk and elated with the prospect of her imminent surrender to love to be able to ignore her. She is piqued, but decides that the harder he tries to break the chain, the stronger it will be. She flirts with Belcore and agrees to marry him in a week's time, hoping to provoke Nemorino, who, however, is confident in the power of his elixir.
When Belcore receives orders that he and his men must move on, he persuades Adina to marry him that night. Nemorino begs in vain for postponement of the wedding till the next day, by which time he expects the elixir to have taken effect, but Adina is determined to torment him and Belcore brushes him aside. Everyone except Nemorino accepts an invitation to the supposed wedding.
Scene 1: Inside Adina's farmhouse
Everyone except Nemorino is celebrating. Dulcamara produces a new duet which he sings with Adina. It tells of a girl who refuses a rich suitor because she loves a poor man. When the time comes for the signing of the contract, Adina is annoyed that Nemorino is not present. When the others have danced out, Nemorino approaches Dulcamara, explaining that he cannot wait till the next day for the elixir to take effect. Dulcamara advises another bottle, but Nemorino has no more money. When Belcore learns of his problem, he explains that he will receive cash immediately if he enlists. He does so, to the amusement of Belcore at having enlisted his rival.
Scene 2: A courtyard
Adina's friend Giannetta tells the village girls that Nemorino's uncle has died and left him a large fortune and they all flock around him. Not yet aware of the news, he attributes his sudden popularity to the elixir. Adina is angry at his apparent desertion of her and Dulcamara wonders if he has accidentally hit on the real elixir of love. When he explains to her that Nemorino had bought the elixir from him to win the heart of some unfeeling beauty, Adina realises that Nemorino really loves her and is remorseful at her treatment of him. Perceiving that she loves Nemorino, Dulcamara decides that she needs a dose of the potion to bring him back to her, but she assures him that she needs no elixir other than her own beauty, which Nemorino is powerless to resist.
Nemorino has seen tears in Adina's eyes and believes she will soon be his, but pretends to be indifferent, telling her he is unable to choose between the village girls clamoring for his attention. She tells him that she has bought back his freedom from the army because he is needed in the village, but is reluctant to admit to her love until he announces that he will still become a soldier if she does not.
Belcore soon recovers from his rejection, declaring that there are lots more fish in the sea. Dulcamara points to the success of his elixir and is besieged by eager customers.