Heroish is a drug you can buy from a merchant in the lower-left of the Ravinale Marketplace. It increases your Psy Defense by 30% and Psy Power by 30%, which in turn increases your health and psy points. The effects are only temporary, however; how long they last depends on how much you buy. You can buy a small pouch for 100 gold, or a large pouch for 250 gold. A small pouch lasts for 2 battles, while a large puch lasts 6 battles. You will be informed when the Heroish wears off.
Heroish is highly addictive. Any time you use heroish, there is a 50% chance that you will become addicted to it. When this happens, you must buy more heroish or begin to suffer negative withdrawal effects. First, you lose 2 hp and 2 psy points. Then you loose one speed which it seems you can't regain any other way than by using more. You will be informed when you are addicted, and when you suffer withdrawl symtoms.