Stranglethorn Brew is the July brew from the Brew of the Month Club.
All members of the Club get free sample of the brew in their in-game mail at start of July. Should you want more, your local Brew of the Month Club Brew Vendor sells it in stacks of six till the end of July.
Like any weak alcohol, this makes you slightly drunk. Also, like all Brew of the Month brews, drinking one of these will create a Empty Brew Bottle that can be targeted and thrown.
With the usual random chance, you get Jungle Madness; a green haze closes in from the sides of the screen and small jungle gnomes threaten you. You do the /cower emote.