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1.
The state of euphoria that one feels after eating Xanax.
Wow, that last bar left me XANTASTIC!
by juicyjay4200 July 09, 2010
 
2.
a: focused, alert, relaxed and calm, wide awake, but not hyper, smiling

b: exceedingly great

c: conceive or seemingly conceived by taking XanoLean
I feel Xantastic!
by AmyP February 08, 2012
 
3.
to be under the influence of xanax and feel absolutely care-free and fantastic.
After a very stressful day at work, Susan took a Xanax to relax. After about 5 minutes the stresses of life seemed to fade away into oblivion leaving her feeling fucking xantastic.
by nunyabiznus May 03, 2012