Muscle relaxants such as Cyclobenzaprine (Flexeril) and Orphenadrine Citrate (Norflex) have also been studied in the treatment of fibromyalgia. Cyclobenzaprine has a tricyclic chemical structure similar to Amitriptyline, yet its anti-depressant effects are minimal. It is used only as a short-term muscle relaxant.ommon side effects of Amitriptyline may include morning sedation, dry mouth, confusion and urinary retention. Fibromyalgia patients seem especially sensitive to these side effects. Therefore, the dose should be individualized and generally begun at the lowest possible dose (such as 5 to 10 mg) at nighttime.