An elixir is an item that a character can drink that will apply an effect to the imbiber. Elixirs can be created by characters with the alchemyprofession, available as drops or from vendors or as quest rewards. Some elixirs provide stat improvements while others provide other effects. Elixirs have a cooldown of three seconds. Some elixirs count as a Battle Elixir or a Guardian Elixir. Battle elixirs generally increase your ability to affect others (+strength, +spell power, +healing), and Guardian elixirs generally affect your ability to affect yourself (+armor, +mana regen, +int). Guardian elixirs do not stack with other guardian elixirs and battle elixirs do not stack with other battle elixirs. This means if you currently have the effect of one battle elixir, and you consume another battle elixir, the new effect will replace the old one. You can only have one battle and one guardian elixir active at one time.
Additional info:
Flask - A more powerful type of elixir in which effects persist through death, and counts as both a guardian elixir and a battle elixir.
Potion - Similar to elixirs with differing effects that are mostly instantaneous or have short durations.
[Elixir of Mighty Agility] [Elixir of Major Agility] [Elixir of the Mongoose] [Ground Scorpok Assay] [Elixir of Greater Agility] [Elixir of Agility] [Elixir of Lesser Agility] [Elixir of Minor Agility]
[Elixir of Mighty Strength] [Juju Power] [Elixir of Major Strength] [Elixir of Brute Force] [R.O.I.D.S.] [Elixir of Giants] [Elixir of Ogre's Strength] [Elixir of Giant Growth] [Elixir of Lion's Strength]
+58 Spell power
+24 Spell power and +24 Spirit
+24 Spell power and +24 Spell critical strike
+35 Spell power
+20 Spell power
+15 Spell power against Undead
Items marked with a * are not classified in-game as a Battle Elixir
Guardian Elixirs[]
Elixir
Effect
Duration
Level
Source
[Elixir of Mighty Thoughts] [Juju Guile] [Elixir of Draenic Wisdom] [Cerebral Cortex Compound] [Elixir of the Sages] [Elixir of Greater Intellect] [Elixir of Wisdom]
+45 Intellect
+30 Intellect
+30 Intellect and +30 Spirit
+25 Intellect
+18 Intellect and +18 Spirit
+25 Intellect
+6 Intellect
[Elixir of Mighty Fortitude] [Elixir of Major Fortitude] [Lung Juice Cocktail] [Elixir of Fortitude] [Goldenmist Special Brew] * [Elixir of Minor Fortitude]
[Elixir of Protection] [Elixir of Major Defense] [Crystal Ward] [Elixir of Superior Defense] [Elixir of Greater Defense] [Elixir of Defense] [Elixir of Minor Defense]