Drugs play a prominent role in many video games. They can range from a skill booster, to health restorative, to a simple part of the narrative. No matter what their cause, they can be a powerful element in a game.
Drugs as Narrative Devices
Many games in the action crime genre, such as Grand Theft Auto, base their some of their missions around drugs. The player is often tasked with transporting some amount of an illegal drug, or helping a group of drug dealers, or assisting in the selling. The drugs, however, are usually kept unseen and act only as a cause for the mission, because driving a truck from Point A to Point B is meaningless unless there is something of value in the truck. The opposite of this would be cracking down on a drug dealer, which was a sub-plot in the classic visual adventure game Portopia Serial Murder Case.
Drugs for Skills
Some games use drugs as a means for accessing skills. Bioshock, for example, uses " plasmids" that the player injects into their veins in order to use their abilities like shooting fire or electricity or bees. Other games, such as Haze for example, use drugs to allow the player to go into bullet time, or increase accuracy.
Drugs for Stat Alterations
Another common role for drugs in games is for altering stats. These games, often role-playing games, have players on missions not focused on drugs, but drugs are found, and used to boost health, temporarily raise other stats, or decrease negatively impacting stats. The XZR / Exile series was controversial for replacing the traditional potions and medical herbs with drugs that the player character consumes to restore health and increase other attributes, though there are side-effects for using them. Fallout 3 has the player use drugs to decrease the damage of radiation and to restore health to body parts, in addition to several drugs which can temporarily boost player stats but risk giving them addictions.