- "Just 5 milligrams today, 5 milligrams tomorrow and a person would sell their first born for 1 milligram more."-- Sid Barry
Flash is a highly addictive stimulant drug that is administered "per oculo", or, by eyedrop. Taking effect quickly, the user becomes "...smarter, faster, and better...", in the words of Beka Valentine, for the duration of the drug's effect. Due to the nature of the drug, addicts use the drug to the exclusion of all else, including food, and generally to the point of an overdose, which can be fatal. The withdrawal is very painful, and sometimes lethal upon occasion.
Flash is produced using an unknown proprietary formula that was developed by Sid Barry (Sid Prophet/Profit) and Ignatius Valentine: it is only known that the Human (and presumably Nietzschean) neurotransmitter acetylcholine is a primary reagent, and the finished product may be a modified form of the same.
It resembles a version of the Earth drug amphetamine, or one of its derivatives, such as methylamphetamine - drugs that are similar in overall effects (cognition and reflex enhancement, paranoia, appetite suppression, etc.), and in the "binge effect" that makes users "tweak" constantly, to the neglect of food and to the point of overdose.
Flash differs in potency, method of administration, and physical addictiveness from Terran stimulants (as Earth-based stimulants are not physically addictive, and the only Terran drugs that are known for causing death in withdrawal are sedatives and narcotics - alcohol, barbiturates, benzodiazepines and opioids), but otherwise is similar. The side effects are feeling of invincibility, arrogance, paranoia, and violent behaviour, again similar to the Terran stimulants amphetamine and cocaine. People would even kill their own families to obtain it when on a binge.
Beka Valentine was once an addict, and, having recovered, struggles throughout the series with at least occasional cravings for the drug.
The sign of a person under the influence is white eyes, with the only color being in the pupil, disregarding the behavioural abnormalities it causes.
- Flash is also used in "Continuum".