An Overload is an untradeable potion bought from the Nightmare Zone. It may used only in the Nightmare zone.
Drinking a dose causes 50 Hitpoints of damage over the first few seconds in five 10 damage increments and constantly applies the extreme potion boosts for 5 minutes. If your stats are lowered while under the effect of an Overload, they will be re-boosted every 15 seconds by the same amount. When the effect wears off, the 50 Hitpoints are not restored. You will be given a message in you chat box when the potion is about to run out.