Great potion which is fully justified and almost poetic in its final results. Taken to quell the flames of emotion, when they can be subdued no longer it bursts into flames. Awesome!
Since most have already taken the potion, the bursting into flames of their neighbors may not bother them too much. Until finally their own fear of it may overtake them and they burst into flames. Crazy countryside where everybody is a ticking time bomb with an unknown amount of time on the clock. Crazy.
An ingenious invention, without a doubt, and perfect for a dystopian fantasy session, much like the series of games I'm planning to run which mix magic and tech. In this setting, the two main sides are based off of Communist China and NATO/ the UN, but there are numerous smaller, third-world nations between the two belligerents who would pay top dollar for a product like this. One angle might be that the players are working fro the Covert Actions Directorate (pretty much the CIA), and they're tracing a shipment of this potion in order to assassinate some enemy leaders or something. Or, if you're feeling REALLY grimdark, the player characters might actually be assigned to administer the stuff secretly to a rebel leader.