Potion

Potions are future craftable food items that confer specific effects in Minecraft. Potion recipes have not yet been defined as of the Beta 1.9 Pre-release. Potion effects were initially introduced in Beta 1.8. Potions will be brewed using special crafting functions in Cauldrons. If Potions are hacked into the game and their damage value is changed, they will acquire effects.

History
Alchemy was first hinted at in July 2010, when Notch explained why redstone ore disintegrates into "dust". He states that dust will be used later in potions.

A couple months later, Notch did a Q&A session on Reddit. He was asked about Alchemy, and responded "Oh Yes! Definitely!". All of his posts in that thread are now deleted, but records can be found in other places.

Potion effects were introduced in Beta 1.8. Jeb later tweeted a screenshot showing potion durations and Glass Bottles taken from within from Beta 1.9 Pre-release 2.