Her drug, which is also called Blood Rush, is a pretty high-class drug that is difficult to produce. It requires a lot of human flesh, so Blood Rush herself needs a lot of suppliers. This has made her clash with Slasher many times before.
Slasher doesn't produce his drug himself. He has a subordinate that converts human flesh into a gene-unraveling drug that grants euphoria and a temporary, but strong boost to strength.
The drug is called Joy, and it is clearly bad for one's health. Anyone that uses it once will get addicted to it. Their gene chain will break after that one use, so they will need more of Joy to fill in the gaps and hold them together for a while.
But that will only delay the inevitable. Eventually, the user will become insane and go on a killing spree using the boost to their strength with no regard for their lives.