The DEA executed a search warrant at Lowell Animal Hospital, 17615 Morse St., taking a close look at a cough prescription for dogs.
The animal hospital was shut down for a few hours.
Lowell Animal Hospital says agents thought a cough medicine was being prescribed too frequently.
Hospital officials said a review of their records showed the prescription fell in line with dosage instructions and gave agents the information they needed.
The DEA says it was investigating alleged diversion of controlled substances and will release more information later.
The animal hospital has since reopened.