Chems were a pre-War term used to describe narcotic drugs and substances that caused numerous temporary side-effects, both positive and negative. Pre-War narcotics include: Mentats, a pre-War "party-drug", originally developed by Med-Tek for medical purposes;Buffout, a "sports-enhancement" drug popularized by athletes;Psycho, a combat-enhancement drug developed per orders of General Chase; and Med-X, a painkiller found in many hospitals. A large drug-trade existed within pre-War society. Skylanes AirFlight 1981 was one of several illegal smuggling operations that utilized jet airliners to smuggle goods across the country.
Little is known about how chems entered the markets of post-nuclear America, though it is commonly accepted by most wastelanders that the Khans invented the chem trade, specializing in the manufacturing of Jet and Psycho. This ability was taught to them by the Followers of the Apocalypse, sometime between 2278 and 2281.
Various chems exist in the wasteland, some more beneficial than others. Each chem has an individual profile, allowing users to "stack" chems to provide a larger bonus than either does individually. Chems may have four or five simultaneous effects, usually with some kind of balance: It might lower one stat while raising another. Abusing chems results in addiction. Addiction to a chem will cause withdrawal symptoms when the chem wears off, resulting in lowered stats unless the user continues to take the drug, or seeks a cure or treatments.
Chems are divided into two groups: addictive, and non-addictive.
Chems can be found lying about individually or inside containers. They can also be purchased from wasteland vendors. While nearly every vendor will have at least a few stimpaks for sale, some chems will need to be purchased from one of the vendors specializing in chems.
Don't take chems. It is never necessary to take chems, so prevent addiction by never taking them at all.
Select the Chem Resistant perk or trait. This perk confers a 50% resistance to the addictive effect of individual chems. Chems which normally have a 10% addiction rate will be reduced to a 5% rate. If the trait is taken, however, chems will only last half as long.
Take a chem antidote. Only the dangerous Jet has an antidote, though. Fixer is also viable (It is intended to be temporary but is currently bugged and provides permanent addiction removal).
Once addicted to a chem, the user has to either continue taking the chem or suffer withdrawal effects specific to the addiction. It is eventually desirable (if not necessary) to cure the addiction. To cure an addiction, the individual has several choices:
Wait it out. Quitting cold turkey will eventually purge the addict's system of the chem. However, Jet addiction cannot be shaken this way, nor can tobacco.
Seek out a wasteland doctor and pay them a fee to alleviate the addiction.
In the release of Fallout 3 in Australia, the game was banned for including references to real drugs. A report was released by the OFLC on why it banned the game. The following is a part of a report that was released:
“The game contains the option to take a variety of "chems" using a device which is connected to the character's arm. Upon selection of the device, a menu selection screen is displayed. Upon this screen is a list of "chems" that the player can take, by means of selection. These "chems" have positive effects and some negative effects (lowering of Intelligence, or the character may become addicted to the "chem"). The positive effects include an increase in Strength, stamina, resistance to damage, Agility and hit points.
Corresponding with the list of various "chems" are the small visual representation of the drugs, these include syringes, tablets, pill bottles, a crack-type pipe and blister packs. In the Board's view, these realistic visual representations of drugs and their delivery method bring the "science-fiction" drugs in line with "real-world" drugs.”— OFLC
One of the reasons for the ban was that the controlled drug, morphine, was one of the chems that would have been available in-game. As a result of the ban, Bethesda decided to have it renamed to Med-X. Evidence of this last-minute change is the fact Med-X's editor ID is Morphine and Med-X addiction's editor ID is WithdrawalMorphine.