Flexeril (or cyclobenzaprine), a muscle relaxant designed to decrease muscle pain, is generally intended for short term use. According to RxList Flexeril is not addictive but it can cause withdrawl symptoms when discontinued. Addiction implies a psychological compulsion to use a substance; withdrawl, on the other hand, concerns side effects which can occur when a substance is discontinued. A compulsion to use a substance is not part of withdrawl.
You can find more about Flexeril at the URL below:
http://www.healthcentral.com/chronic-pain/find-drug-25215-25.html