Scramble is a euphoric designed more or less accidentally by CIA-sponsored pharmacists in an attempt to create a better class of interrogation enhancer. Its intended effect was to intensify memory, but although that is indeed one of its effects, it does so in a way that is more or less useless for interrogation purposes.
Scramble brings back good memories accompanied by a euphoric high, which often makes its users appear very withdrawn and physically uncoordinated. But after a peak is reached, a downward cycle begins: the memories become progressively less pleasant and the euphoric effects slowly turn depressive.
Despite this, Scramble is at least as addictive as most opiates, and has similar physical effects with long term use. It is also quite potent: a single kilogram of Scramble will last even a heavy user for a year and then some.