A study of patients at pain or rehabilitation clinics who were prescribed opioids found 20 percent tested positive for the anti-seizure drug gabapentin (Neurontin), even though they did not have a prescription for the drug.

Gabapentin is also used to treat nerve pain, HealthDay reports. While the drug poses little risk for abuse and addiction when taken alone, it can increase the high a person gets from opioids, the article notes.

“The high rate of misuse of this medication is surprising and it is also a wakeup call for prescribers,” study author Poluru Reddy said in a news release. “Doctors don’t usually screen for gabapentin abuse when making sure patients are taking medications, such as opioids, as prescribed. These findings reveal that there is a growing risk of abuse and a need for more robust testing.”