Entrance to a farm. In a Basque village, the harvesters shelter from the summer heat in the shade of a large tree. Adina, a beautiful and rich tenant farmer, sits by herself reading a book. Nemorino, a young peasant who is in love with her, observes her from a distance and despairs of ever making a breach in her heart. The peasants are curious to know what Adina’s book is about and ask her to read it aloud to them. She sits down in their midst and reads them the story of Tristan and Isotta, who fell in love as the result of a magic philter. Naturally, they all want to know the recipe for the magic elixir. The roll of a drum announces the arrival of a garrison of soldiers, led by sergeant Belcore. The sergeant offers a bunch of flowers to Adina, pays court to her and, without more ado, asks her to marry him. Flattered and amused, Adina coquettishly encourages his advances but is certainly in no hurry to accept the sergeant’s proposal. When Belcore goes off, Nemorino, who has been watching the scene in despair, declares his love. Adina once again rejects him, on the grounds that she is too capricious to embark on any serious engagement. In vain she attempts to discourage the lad from loving her. The village square. A trumpet heralds Doctor Dulcamara, a crafty quack doctor, who arrives in a gilded carriage. As the villagers gather round, he offers them a miraculous drug, an elixir that cures all ills. The villagers all rush to buy his precious liquor. After the crowd has dispersed, Nemorino approaches the doctor and asks him if he possesses the elixir that once caused Isotta and Tristan to fall in love. For a ducat Dulcamara sells him a bottle of Bordeaux, passing it off as an elixir of love. He points out, however, that its effect is not immediate and that he must wait twenty-four hours, thus allowing himself plenty of time to get safely away. The simple Nemorino goes into ecstasy and drinks the elixir, under the illusion that Adina will fall in love with him. The girl now happens to approach him and notices how very lively he has become. She is surprised, also, at his affected indifference and her hurt vanity inspires her to plan revenge. Belcore returns and renews his proposal of marriage to the lovely Adina. Still vexed at Nemorino’s sudden coldness, she accepts. She will marry the sergeant in six days’ time. Nemorino is not worried by this news, as he knows that on the following day the elixir will produce its effect. But Belcore has received orders to leave the village with his platoon. Adina decides therefore to marry the sergeant that same day. Nemorino attempts to convince her to wait at least until tomorrow. But Belcore is irritated and starts to threaten the young peasant, until Adina puts an end to this awkward situation by inviting them both to her house, to celebrate the forthcoming marriage with a banquet. 

The guests toast the betrothed couple while Dulcamara strikes up a barcarole with Adina on the theme of Nina, the beautiful girl gondolier, who rejects the courtship of a rich senator because she loves the young Zanetto. The notary now enters to draw up the marriage contract. Adina however, who is irritated by Nemorino’s absence and would like to spite him by signing the contract under his nose, decides to put off the wedding until the evening. Nemorino in despair returns to Dulcamara and asks him how he can speed up the effect of the elixir. The charlatan replies that he must increase the dose; but if the young man wants a second bottle, he must of course pay for it. Penniless by now, Nemorino accepts a request from his rival Belcore to enlist in the army. Having received twenty ducats in payment, he dashes off to buy a fresh does of the elixir. A village courtyard open at the far end. Giannetta recounts the latest news to the village women, that a rich uncle of Nemorino’s has just died and left a will making him his sole heir. Nemorino appears, still unaware of this turn of events and having just drunk the second bottle of Dulcamara’s elixir. When all the village girls surround him and pay court to him, he believes this is the effect of the elixir. Adina and Dulcamara contemplate the scene in amazement. The girl would like to talk to Nemorino and dissuade him from enlisting as a soldier. But the other young women drag him off to dance in the courtyard. Adina then learns from Dulcamara the reasons for Nemorino’s behavior and for his decision to join the army. She feels remorse now and, believing that she has lost him, realizes that she loves him. Dulcamara offers his elixir to her too, but Adina refuses it, preferring to trust her own charms to recapture the young man’s heart. Nemorino returns from the dancing, but grows sad at the thought of the tear that he saw fall from Adina’s eyes when his attentions were focused on the other girls. Adina tells him she has bought back his freedom by repaying Belcore the twenty ducats received for his enlistment, and finally confesses that she loves him. The two are reconciled, while Belfiore stands aside. All the villagers gather round Dulcamara and pay homage to the supreme virtue of his elixir.