Veterinarians don’t typically prescribe some of the most commonly abused opioids, like oxycodone and fentanyl, but do dispense other heavy drugs like hydrocodone, a semi-synthetic opioid often used to treat nagging coughs in dogs, and alprazolam (Xanax), an addictive benzodiazepine used to treat household animals for anxiety stemming from thunderstorms, fireworks and vacuum cleaners.

The most common drug carried by vets and targeted by addicts by far, however, is tramadol, an opioid pain medication prescribed to both animals and humans.

In recent years, as the opioid crisis in the U.S. has worsened, vets say they’ve seen an increase in the number of patients who are making repeated visits to their offices in search of such drugs, prompting some states to add them to a list of prescribers required to report suspicious activity.