I have not took flexeril (cyclobenzaprine hcl) in four days will it show up in a drug test?

Possibly. The rate of drug elimination from the body is called the half life; it is the time for half of the dosage to be eliminated. After two half lives, only 1/4 of the amount will be present. The half life of cyclobenzaprine ranges fro 8 to 37 hours, and is affected by many other medications however, cyclobenzaprine is not a drug of common abuse, and would not likely show up n a drug abuse screen.