Poison

Along with lava and spikes, poison is among the oldest and most common tropes in videogames.

The virtual world can be a hostile place filled with poisonous pits, plants, mushrooms and animals. Well known examples include:

• Venoms - injected into the body by insect stings or animal bites
• Toxins - natural poisons found in toxic mushrooms, berries, dead animals or rotten food
• Nerve Agents - human-produced and deployed gases & chemicals
• Chemical - naturally occurring and deadly, like arsenic
• Radiation - coming from microwaves or radioactive zones
• Soundwaves - explosions, flash-bang grenades. Not a poison per se, but effects are similar and also part of toxicology

Effects

Effects of poisoning in games can show as a change of skin color, vignetting, blurred or doubled vision, slowed perception of time, obstructed movement, loss of consciousness and ultimately loss of life.

The most basic example of poison can be traced to games inspired by Dungeons & Dragons, such as Final Fantasy. When afflicted with poison characters lose a small amount of health (small in that it is less than would be received from a standard enemy attack) every turn until they are cured of poison.

Green is the color most associated with poison, whether it is a poison cloud, poisonous enemy or the player's health bar has been turned green to indicate poisoning.

Examples of Interesting Game Mechanics Resulting from Simulation of Real Poisoning

Exposure

Exposure to poisons is either acute like the bite of a snake or chronic like the long term effects of radiation from nuclear fallout inside the Zone around Chernobyl. Radiation poisoning can also be acute like the microwave tunnel in Metal Gear Solid 4 or hard gamma and X-rays in proximity to a reactor.

Neurotoxins are often utilized to increase the lethal effects of ranged weapons like blow darts (see Assassin's Creed) or they are administered stealthily via syringe.

Antidotes

To counteract toxic effects health potions or antidotes are available. Eastern European franchises like S.T.A.L.K.E.R. and The Witcher prominently use alcohol as both an intoxicating agent and an antidote.

Even though classically "only the dose makes a thing not a poison", not many games make use of this fundamental principle. Apparently all videogame poison is a really, really high dose.