Antidroga literally translates to "anti-drug". It's a striking and somewhat unusual word to find in a pop song, making it memorable.
In the context of the song, the artist uses "antidroga" metaphorically to describe the intense, almost addictive, nature of a relationship. The person's eyes are described as the "antidroga," implying that their presence is a powerful, perhaps even dangerous, remedy or escape from reality, much like a drug itself. This paradoxical use creates a compelling image.
Emma spends this whole song admitting she cannot quit someone. "So bene che ti amo" [I know I love you] arrives with a list of exceptions that turn out not to be exceptions at all: "Compreso quando ti odio" [Including when I hate you], "Compreso quando fai l'offeso" [Including when you sulk]. Then the title lands. His eyes, she sings, "Mi inseguono come se fossero l'antidroga" [chase me as if they were the drug squad], which makes him the substance and makes loving him the thing the police are meant to stop. The best line here is quieter than any of that: "Ma ora siamo più soli di una piazza vuota" [But now we are lonelier than an empty square].
Fabri Fibra shows up halfway through and moves the metaphor into a nightclub, where the vodka keeps coming and "Che ci fai tu qui sola? La consolle ci consola" [What are you doing here on your own? The DJ booth consoles us] is a pun he clearly enjoyed writing. He signs off with "Faccio un tiro, chissà cosa si prova" [I take a drag, who knows what it feels like] and then "Finisco prima che arrivi l'antidroga" [I'll be done before the drug squad shows up]. Nobody here is having a good time, and nobody is leaving.