In a small California farming community, Giannetta and the rest of the workers rest at midday. Nemorino, a dairy worker from a neighboring ranch, sighs as he gazes at the intelligent and alluring land owner, Adina, with whom he has been in love for years. Reading to her friends the story of Tristan and Isolde, Adina wittily reacts to the mention of the magical love potion that melted Isolde’s cold heart, making her fall instantly in love with Tristan. The scene is interrupted by the bombastic arrival of a small group of militia led by an extremely self-assured sergeant, Belcore. The sergeant begins to boldly express his love for Adina, which distresses Nemorino as he is much too shy to do the same. Adina welcomes the soldiers to stay in their village but warns Belcore that her heart is not so easily won.
As the crowd disperses, everyone returning to their labor, Nemorino timidly asks for a word with Adina. She tells him he should stop mooning around the village, that she is far too capricious for him to keep fawning over, and that he should hurry on to visit his sick uncle who lives in the next village. Nemorino declares that it is impossible for him to leave, but Adina leaves him with little hope.
Suddenly, a train is heard in the distance and the villagers gather again to welcome the mysterious Dr. Dulcamara who is selling an elixir that promises to cure every ill from bed bugs to wrinkles. Nemorino approaches the doctor, asking if he knows anything of the famous love potion from the story of Tristan and Isolde. Dulcamara insists it's he alone who makes that potion. Overcome with joy, Nemorino buys a bottle (which, Dulcamara tells the audience, is actually wine) and hurries off to take his dose.
Adina notices a change in Nemorino, who has newfound confidence, having been promised by the doctor that the potion will take effect after one day. Vowing to make Nemorino jealous, Adina agrees to marry Belcore in six days. Nemorino laughs, knowing that by tomorrow Adina will have eyes only for him. Just then, a messenger arrives with a letter containing orders for Belcore to move out the very next day. Bewildered by Nemorino’s laughter, her scheme having seemingly failed, Adina tells Belcore she shall marry him that very day. This time it works - Nemorino is devastated.
Later that day, as the village convenes for Adina’s wedding, Nemorino is nowhere in sight. Adina is disturbed at his absence and sends the group to enjoy the feast, delaying the ceremony despite the arrival of the notary. Nemorino seeks out Dulcamara in his despair, asking him what to do. The doctor says the solution is certainly another dose of elixir, but Nemorino has already emptied the bottle. He asks to purchase another, but has no money to pay for it. Dulcamara gives him fifteen minutes to find the funds, as he exits to go prepare to leave town. Nemorino is wondering what to do when Belcore appears and suggests that the quickest way to earn venti scudi is to join the army. Though he has no interest in the life of a soldier, Nemorino signs the contract and runs off with the money to find Dulcamara.
At the wedding banquet, Giannetta gathers a group of friends to share the news she just heard about Nemorino - his rich uncle has died, leaving Nemorino his fortune and making Nemorino the most eligible bachelor in town. When Nemorino appears, drunk from his second bottle of “elixir,” the same people who formerly scorned him are now the ones fighting over dancing with him. Adina observes this with sadness, even shedding a tear (which, unbeknownst to her, Nemornio sees as he is whisked off to the dancing). Finding Adina upset, Dulcamara offers to sell her a bottle of elixir. She refuses, saying her charms are the only elixir she needs. Instead, she buys back Nemorino’s military contract and hands it over to him along with a profession of her love. Belcore, seeing the two together, departs, saying there are plenty of other fish in the sea, and Dulcamara takes the credit for the lovers’ union