Used to be able to but when Realm Reborn debuted this option was no longer in the game. I have heard members of my FC speaking of changes coming to Potions and I have noticed the cool down timer has been reduced since I have came back to the game. Used to be /item "Potent Poison" or along those lines. Its been ages since. I hope they introduce this option again as my old Macro as a Healer was to run up and use poison and say something about crushing it as a DPS Healer along with "Pop a top again"