The quad temporarily multiplies all your weapon's strengths by

four times. Let the gibbing begin!

—The Quake II Manual

The Quad Damage (aka Power Amplifier) in Quake II is a Powerup that amplifies a weapon’s damage by a factor of 4 (quadruples). Even the most basic weapons with it, such as the Blaster, can do incredible damage, usually able to take out a target with one or two shots. It is the most sought-after Powerup in Quake II.

In Single Player, it can be stored in the inventory when picked up and used whenever you feel like it. Only 1 can be held at any one time on Hard skill, 2 in Medium skill level, so it is advisable to use them as they come as the player will lose out on the Quad Damages he/she comes across if he/she already has one clogging up space in their pack. It does however mean that they can be used when and where the player sees fit, such as a boss fight. This does not apply on Easy skill, where unlimited Quad Damage powerups may be held at any given time.

In Multiplayer, the Powerup is instantly activated after being picked up unless the Instant Powerups deathmatch flag is set to false. (Instant Powerups has a dmflags value of 16)

In the CTF modification (available in a Quake 2 3.20 update bundle) the player with the quad glows the color of his respective team.