It is not necessarily unsafe to take the drugs Cymbalta (duloxetine) Flexeril (cyclobenzaprine) together. Cymbalta is an anti-depressant that is also used to treat pain in patients with fibromyalgia and
neuropathy, while Flexeril is a muscle relexant used to treat to pain in patients with some muscle conditions, so it would not be rare for someone to be prescribed both medications concomitantly. Both drugs can act as central nervous system depressants (drugs that causes a slow down in brain activity such as alcohol), according to www.drugs.com a person taking both of these medications at the same time should take caution when engaging in activites that require mental alertness or coordination such as operating a motor vehicle or machinery until they know how the medications affect them. The site also advises patients to notify their physician if they have excessive CNS effects. A 2006 abstract from the Mayo Clinic does reference a rare condition called serotonin syndrome which can result from taking Cymbalta, Flexeril and other proserotoninergic medications together with mild to possibly lethal implications.