EVE

From BioShock Wiki

EVE is a glowing bluish serum that you inject into yourself which allows the use of plasmids. It's found throughout the city of Rapture in hypodermic needles. It is similar to "mana" in fantasy RPG's. EVE Hypos can be bought at most Circus of Value vending machines.

EVE is a modified version of ADAM, and while ADAM gives the ability to carry plasmids in the body, EVE gives the power to use them. It was probably developed by Yi Suchong, in his study of plasmids and genetic modification. It is not certain why EVE is so common and ADAM scarce.

The first design of the EVE Hypo (as seen in the "Bringing it Home" gameplay trailer), was a smaller, leaner needle full of a green murky liquid.

[edit] Trivia

• EVE and ADAM are a reference to the biblical characters Adam and Eve, who were granted immortality in the Garden of Eden until they fell from grace. This parallels the fall of Rapture and its citizens.