The poor and bashful Nemorino is hopelessly in love with the rich and beautiful Adina. He hears her reading aloud the legend of Tristan, who has won the heart of Queen Isolde using a magic love potion. While Nemorino is dreaming about this magic potion, soldiers under the command of Sergeant Belcore enter the village. Adina immediately attracts the brave warrior's attention. He does not plan to hang around long: let Adina name the wedding day immediately! And yet the girl dislikes the sergeant's self-assurance. She cunningly and coquettishly spurns the advances of her unlucky admirer. Seizing the moment, once everyone has left, the unhappy Nemorino hastens to declare his love for Adina, but the mischievous imp tells him that faithful and constant love is not for her.
The itinerant medicine man Dulcamara, a charlatan and scoundrel, arrives in the village. The sales of "miracle-balsams" are well underway. The unfortunate Nemorino, too, turns to him for help: "Do you not have Isolde's love potion?" Pleased to be addressing such a simple fellow, Dulcamara gives the youth a bottle of everyday Bordeaux and promises that the "elixir" will act within a day, calculating the amount of time he needs to get far away from the place. Nemorino's impatience is so great that he immediately drains the bottle of its "elixir of love". He believes that the potion is having an immediate effect. Confident that Adina will soon fall in love with him, Nemorino feigns coldness. Such novel and unexpected behaviour from her admirer wounds the girl's pride. The arrival of the sergeant gives her a hint as to how she can repay Nemorino. She promises her hand to Belcore. Suddenly the sergeant receives the order to abandon the village. Adina agrees to hold the wedding that very day. Nemorino's head is instantly cleared of tipsiness. Understanding that he is losing his love forever, the luckless youth begs her to postpone the wedding at least until the next day.
Preparations for the wedding are underway, and the guests are drinking and having fun. Dulcamara asks Adina to sing a new song for two voices with him – a barcarolle about a senator and a boatwoman. Reeling at the news that the notary has appeared, Nemorino begs the doctor to save him – to make the people fall in love with him before the next day arrives. Naturally, the charlatan recommends that the youth purchase another bottle of the elixir – to increase the potency of the drink. In order to earn money and acquire his next dose of the potion, Nemorino becomes a recruit in Belcore's regiment. Holding the precious coins in his hands, he hastens off to find Dulcamara.
News unexpectedly flies around the village: Nemorino's uncle has died in the city, leaving him his entire fortune. Only Nemorino, emboldened by the second portion of the doctor's "elixir of love", is unaware of these events. Dulcamara guarantees that this time the drug will definitely work, and the lad is filled with the most glittering expectations. On his way, indeed, the first girl to meet him – Giannetta – pays heightened attention to him because now he is a rich single man. Dulcamara is amazed. It would appear that the contents of the bottle truly are magic. Adina witnesses Nemorino's unprecedented success with the ladies and learns that he has joined up to be a soldier to win her heart. Dulcamara, seeing Adina's jealousy, offers her his elixir of love. But the beauty has no need of the sorcerer's services, she having an elixir no less powrful than his: "The recipe is written on my face, the potion in these eyes".
Nemorino's drunkenness has passed, and again he laments Adina. The tear of offence in her eyes tells him that he, too, is loved. At the same time, Adina purchases the recruit list from Belcore. She hands the contract to Nemorino, persuading him not to leave his home village. The youth is disappointed: he had expected a declaration of love. "As no-one loves me, I'd rather die a soldier!" he exclaims. The perturbed Adina at last opens her heart and falls into the arms of her beloved. Belcore is by no means dejected: there are many more women on the face of the earth. Dulcamara is inspired by the success of his curative drink.