Brief answer....FIORICET results in addiction,if used for long periods.
Detailed answer....
Hello,
Thanks for the query.
Fioricet is a brand name for a compounded oral medication containing 50 milligrams of butalbital, a barbiturate, 325 milligrams of acetaminophen and 40 milligrams of caffeine. 
This drug results in addiction if used for long periods.
Withdrawl symptoms occur because of butalbital as well as caffeine.
Withdrawl symotoms of butalbital can be anxiety,insomnia,upset stomach,nausea,nervousness,irritation and sometimes convulsions also.
One should not quit it cold turkey,if used for long periods.
One must withdraw from it gradually by gradually reducing the dose.
I hope it helps,however you may revert to me for any specific query pertaining to it.
I would be very happy to assist you.
Best of luck
Thanks

---