Spook is an extremely dangerous drug of unknown provenance found in the Imperium of Man that has sometimes been used to provide temporary psychic powers to those that use it, particularly during combat situations. The drug's effects are inconsistent and are just as likely to lead to psychosis or other forms of mental instability as the development of a psyker's abilities.
Those who fail to gain such abilities often find their mind filled with terrifying visions of the Warp for several solar hours. If the use of spook successfully provides psychic abilities, the rush of power can quickly become addictive, leading to increasing use of the drug.
Saying that foreign drugs such as spook are frowned upon in the Imperium or among its military forces is a grave understatement. Anyone caught with this drug would find themselves on the wrong end of a Commissar's Bolt Pistol, but addicts will be addicts and it is not uncommon to hear tales of an Imperial Guardsman fighting under the influence of spook. The only question he has to ask himself is if the risk of being caught is worth the temporary benefits.
- Only War: Core Rulebook (RPG), pp. 199-200