It's just a fun drop that give you lots of weird effects when you drink it. They sell for about 100r each but they don't really have a use. I've got 5 DCs of them sitting around lol.
You can make potions out of them. I heard that in chat and so I tried it out and it worked. I made any potion I wanted. It wasn't made exactly like a regular potion and I forget now what I did to get it to work. Maybe someone else knows the exact process. I was happy to find a use for them.
There is actually a really good use for them; they could just safe your life. A Zombie virus (see link for wiki page) gives you Resistance IV for 20 seconds, which means that you'll take considerably less damage during that period. But... to make sure it's not too OP you also get several negative effects, mostly cosmetic though (such as Nausea and Blindness). If you want to know about all the Empire custom items then check out this link; this wiki section lists all custom items and also explains what they do
From personal experience, you will find that drinking this potion while wearing decent armor can essentially make you a quasi-god for the 20 second period of time. The benefits make it really hard to take advantage of the resistance. However, if you're in a position requiring some form of damage endurance it can prove very useful.
If you drink it u get dizzy but it can be great for the resistance if you are in trouble! But don't take my word for it
As to me, I just like to drink them for fun, I'm not too sure why They're a pretty cool custom mob drop though, I've got to say.
True, I wish there was a 'town variant' which only had the weird effects and lasted longer (30 or so seconds) I think you could have some major fun during events
