The Drug Enforcement Administration says it found 39 instances in which CVS pharmacists filled prescriptions for Percocet that they should’ve known were forged.

That is a violation of the Controlled Substances Act, which stipulates that pharmacists have a responsibility to ensure that a prescription is valid.

Claire Brennan is an investigator for the DEA’s New England division. She says pharmacists should know how to identify certain “red flags.”

"If someone is continually paying, if they’re coming a long distance to see a particular doctor, if it’s ongoing, [like] the second or third month this person has something from the dentist, that should be a red flag."

In a statement, CVS said it is committed to following federal and state laws. "CVS pharmacists evaluate controlled substance prescriptions," the statement says, "and consider a variety of factors when exercising their professional judgment as to whether or not to fill a prescription."

Brennan says filling forged prescriptions has consequences. For example, some of those drugs can end up being sold on the street.

Her advice to pharmacists: "If something seems questionable, question it."