Drug fueled behemoths
In the early 1990s, a new designer drug hit the streets of Gateway City known simply as “Power” and marked with a pixelated flower (a reference to the “power up” that you can get in Super Mario Brothers). Its effects were to make the user feel a euphoric sense of confidence and was accompanied by reckless behavior and an extreme crash afterwards. Users became addicted to the high and would do just about anything to avoid the crash. This led to numerous overdoses as well as a number of suicides resulting from the crash.
Efforts from law enforcement (and a few underground vigilantes) ended the trade at the same time as use declined after its dangers became more common knowledge. But it did not go away completely.
During those early days, it was discovered that the drug taken in large doses would not only cause the euphoric high, but also make the user tougher and stronger than they normally would be. In one case, the user even increased in mass. However, the amounts needed to gain these effects included a correspondingly intense crash.
Recently, a new version of Power has surfaced, in a more concentrated formula. The high is still there as is the recklessness. This new version also has the effect that it allows the user grow to a considerable size, and with it an increased strength and durability.
In this world of meta-humans, many criminal groups (street gangs, mob henchmen, etc.) have found it very useful, giving their minions a needed edge to continue their criminal activities.