Love poison

During Hearts & Hooves Day, the Cutie Mark Crusaders attempted to play matchmaker for Cheerilee and Big Macintosh. When they failed, they bumped into Twilight Sparkle who informed them how the holiday began with a love potion, and led them borrow the book she'd read it from, which even included the recipe.

Only after seeng the side-effects of the supposed love potion did the CMC read further to realize it wasn't a love potion at all - Rather it was Love Poison.

A long time ago, an earth pony prince made this recipe and gave it to a pegasus-unicorn princess he liked - He'd meant for it to be a love potion but things didn't turn out so well ("Something about a dragon, a kingdom falling, chaos reigning, etc.)because the prince & princess were so lost in each other's eyes they couldn't perform their royal duties.

Recipe
"''Take a tuft of cloud, a bright Rainbow's glow,

Stir with a pegasus feather - Fast, not slow

Serve to two ponies who aren't in the know''"

Cure
If the two lovestruck ponies are kept from looking into each other's eyes for one full hour, the effects of the Love Poison wear off.