"Euphoria, I take it? And what's that I smell? Mmmm . . . you've added just a sprig of peppermint, haven't you? Unorthodox, but what a stroke of inspiration, Harry..."
-- Horace Slughorn (HBP22)
The Elixer to Induce Euphoria is a potion which induces intense excitement and happiness in the drinker, with occasional side effects of excessive singing and nose-tweaking (the addition of peppermint would tend to counterbalance that effect, according to notations by the Half-Blood Prince in Harry’s potions textbook) (HBP22).
References from the canon
When correctly made, the potion is sunshine-yellow (appropriate, being a colour suggestive of cheerfulness) (HBP22)
Instructions to brew this potion can be found in Advanced Potion-Making (HBP22)
From the Web
"Elixir to Induce Euphoria" from Harry Potter Wiki