From Quake Wiki
A quad damage will cause your weapons to dish out four times their normal power. Be careful with explosive weapons, because it's not exactly hard to kill yourself. Every time you hit a wall, it's like shooting yourself dead-on with two rockets. Yeah, ouch. Then again, there's not much that can save a player from even one quaded rocket, so if you're in an open area use them as much as possible. The best alternatives to the explosive weapons are the super nailgun and the thunderbolt - they both do plenty of damage. Just remember that you glow when you have this, so players will know it.
|Items in Quake|
|Health | Ammo Boxes | Mega-Health | Quad Damage | Biosuit | Pentagram of Protection | Ring of Shadows | Green Armor | Yellow Armor | Red Armor|