Adina, wealthy owner of a local farm, her friend Giannetta and a group of peasants are resting beneath a shade tree on her estate. At a distance Nemorino, a young villager, laments he has nothing to offer Adina but love (“Quanto è bella, quanto è cara”). The peasants urge their mistress to read them a story – how Tristan won the heart of Isolde by drinking a magic love potion (“Della crudele Isotta”). No sooner has Adina done so than sergeant Belcore swaggers in with his troop. The soldier’s conceit amuses her, but he is not dissuaded from asking her hand in marriage (“Come Paride vezzoso”).
In the town piazza, villagers hail the traveling salesman Dr. Dulcamara, who proclaims the virtues of his patent medicine (“Udite, udite, o rustici”). Nemorino asks Dulcamara if he sells the elixir of love described in Adina’s book. Pulling out a bottle of Bordeaux, the charlatan declares this is the very draught. Though it costs him his last cent, Nemorino buys the wine and hastily drinks it. Adina enters; certain of winning her love, he pretends indifference. To punish him, Adina flirts with Belcore, who, informed that he must return to his garrison, persuades her to marry him at once.
The pre-wedding supper is in progress. Adina goes off with Belcore to sign the marriage contract; the guests disperse. Remaining behind, Dulcamara is joined by Nemorino, who begs for another bottle of elixir; his pleas are rejected, because he has no money. Belcore returns, annoyed that Adina has postponed the wedding until nightfall; he spies Nemorino and asks why he is so sad. The youth explains his financial plight, whereupon the sergeant persuades him to join the army and receive a bonus awaiting all volunteers (“Venti scudi!”). Peasant girls, gathered in the square, hear from Giannetta that Nemorino’s uncle has died and willed him a fortune. When the youth reels in, giddy from a second bottle of wine, they besiege him with attention; unaware of his new wealth, he believes the elixir finally has taken effect. Adina and Dulcamara arrive in time to see him leave with a bevy of beauties. Hoping to sell Adina a bottle of elixir, Dulcamara claims that Nemorino’s popularity is due to the magic potion. Adina replies she will win him back through her own charms (“Quanto amore!”). Reentering alone in a pensive mood, Nemorino takes heart because of a tear he has seen on Adina’s cheek (“Una furtiva lagrima”). When she appears, he acts disinterested. She confesses she bought back his enlistment papers because she loves him (“Prendi, per me sei libero”).
Attributing Nemorino’s happiness and inheritance to the elixir, Dulcamara quickly sells more bottles before making his escape.