ADAM is a miraculously effective and highly sought-after stem-cell compound produced by a species of deep-ocean sea slug. Discovered by citizens of Rapture, ADAM has been referred to as a genetic canvas, allowing for parts of an individual's genetic code to be re-written and replaced with new information. ADAM quickly became the most valuable resource in the world to the population of Rapture, and gave birth to a thriving industry of genetic modifications, which came in the form of plasmids. Plasmids allowed people to modify themselves in just about any way they saw fit, from curing male pattern baldness to producing sexually appealing pheromones, to granting the powers of telekinesis and mind control. So successful was this plasmid industry that supplies of ADAM quickly began to run dry, with the seemingly endless numbers of sea slugs unable to produce sufficient amounts of the compound to support the thriving industry catering to thousands of individuals. Eventually, a plan was enacted to produce ADAM at the required levels, which involved surgically integrating the creatures into the digestive tracts of little girls. These Little Sisters were essentially walking ADAM factories. Robbed of their humanity, yet gaining a form of immortality, the Little Sisters could heal from almost any wound with remarkable speed, and seemed to never age. As Rapture spiraled out of control in a brutal civil war between the forces of Andrew Ryan and Atlas, so too did the use of ADAM, and the majority of enemies the players encounters-- Splicers--were once normal people, now driven hopelessly insane and horribly disfigured from ADAM abuse.
Usage in the BioShock Series
ADAM is the game's most valuable resource, and is only gained in BioShock by either saving or harvesting Little Sisters. ADAM can be used throughout the course of the game at Gatherer's Garden vending machines, which allow the player to spend ADAM to purchase plasmids, increase or enhance the players existing arsenal of genetic powers. It is not clear exactly what Jack does with the ADAM in order to purchase new abilities, or why he cannot simply use money.
In BioShock 2, in addition to rescuing/harvesting Little Sisters, ADAM can be scavenged off the bodies of defeated Big Sisters, who are also capable of extracting it from corpses, and found in the form of the actual sea slugs which lie on the bottom of the sea and can be picked up directly by Subject Delta as he walks between buildings in Rapture. It can also be found in multiplayer, scattered around the various levels in the form of vials of red liquid. ADAM does not play an active role in multiplayer, but collecting the vials adds points to a player's total score at the end of a game. This total score works towards advancing the player's rank, which allows for access to more plasmids, tonics and weapon upgrades.