I want to drink a potion for the achievement but i love my avatar now is there a cure to any physical changes the potion may make?

Yes. The virus caused by the potion is temporary. How it will go away, we're not sure yet, but no virus has ever been permanent.

Nope, no cure. They are temporary though, so a cure probably won't be needed, it sounds like they'll just wear off on their own. However the changes are pretty minimal so far too. This thread will show you what effects the different potions will have on your avatar at this point.

If you want to cure it right after drinking the vial it's not possible .. If you drink it your Avatar will change to something that's not sure by now but it probably will get away by itself since the Staff said it's temporary ^-^

Edit: because I can't spell properly xD

Thanks gguys! Got that pesky achievement!