Amortentia

"Amortentia doesn't really create love, of course, it is impossible to manufacture or imitate love. No, this will simply cause a powerful infatuation or obsession. It is probably the most dangerous and powerful potion in this room—oh yes," he said, nodding gravely at Malfoy and Nott, both of whom were smirking skeptically. "When you have seen as much of life as I have, you will not underestimate the power of obsessive love."

—Professor Slughorn,
in Harry Potter and the Half-Blood Prince