The Dark Dragon Potion was an elixir and an item the episode "The Tale of the Dark Dragon" of the children's horror series Are You Afraid of the Dark?.
Keith Saunders, a bookworm who had his leg mangled in a car crash and had his outlook on life altered as well, happens upon an advertisement for potions in Sardo]'s magic shop. For $20, Sardo hands him the Dark Dragon Potion, warning him that it's very powerful and that only one drop should be used at a time. Keith decides to test it out by adding a drop to Harold, Sardo's mangy looking rabbit. After watching Harold become less mangy, Keith decides that it works. But shortly after Keith walks out of the shop, Sardo sees that Harold has become a hideous gremlin-like creature.
Back at home, Keith takes a drop of the potion and immediately begins going into convulsions. When they pass, Keith emerges with a different hairstyle and the limp in his leg is gone. But a day later, he soon starts to sprout hair on his chest and face and starts growing fangs. As it turns out, Sardo neglected to read the full warning on the bottle: "Before bringing out the best, one might fight the dark dragon from within".