Hitonatsu no Liter Girl

Tsukifune's looking for part-time work so she can earn money for a vacay with her besties, and gets referred to a cushy hostess job at a bar owned by her rich classmate Narumiya. She suspects that he might have ulterior motives, but lets it slide for the hefty paycheck... and it ends up being Narumiya's lucky day when a lactation-inducing drug has some unintended side-effects on her libido.

(Source: Fakku!)