It’s not an opioid, but a popular pain medication is increasingly showing up in drug overdoses, worrying doctors and lawmakers.

Gabapentin is a prescription medication primarily used to treat seizures and neuropathic pain associated with herpes zoster, otherwise known as shingles.

Since the drug was first approved for use in the United States in 1993, it’s largely been considered safe with little or .

But the opioid epidemic could be changing that.

Gabapentin is now so common among that lawmakers have included it as a controlled substance.

According to data from the coroner’s office in Louisville, gabapentin was found in nearly . Across the state, the drug is now showing up in about 1 in every 3 overdose deaths.

The drug has been dubbed an “emerging threat” in the opioid epidemic by officials there.

It’s sold under the brand names Neurontin, Gralise, and Horizant. It’s been available as a generic in the United States since 2004.

Despite turning up in a significant number of fatal overdoses, officials say gabapentin is likely not the cause of the deaths.

Gabapentin can cause effects on the central nervous system, including drowsiness and low-level euphoria, but nowhere near the extent of opioid painkillers.

It’s far more likely for potent drugs such as fentanyl and heroin to result in death. But combining these with gabapentin can result in an even more dangerous high.

“Gabapentin is not a very potent drug, needing high doses to produce its effects,” Edward Bilsky, PhD, provost and chief academic officer at Pacific Northwest University of Health Sciences in Washington and an expert in opioid pharmacology, told Healthline.

“There has been an increase in the mentions of gabapentin toxicity in emergency rooms, including overdose deaths. These are likely due to a combination of gabapentin with another central nervous system depressant,” he said.

Gabapentin’s reputation

Even before gaining recent attention for its role in the opioid epidemic, had acquired something of a dubious reputation.

While initially only approved for seizures and neuropathic pain, it was widely prescribed and marketed for other conditions and symptoms. Those include bipolar disorder, migraines, insomnia, and anxiety.

It’s also sometimes prescribed for chronic pain.

Pfizer, the developer of gabapentin, was involved in a lawsuit over their marketing of the drug for these off-label treatments. The company more than $400 million in 2004 to settle fraudulent claims it made about the drug’s uses.

It’s common and legal for some drugs to be prescribed off-label. However, it’s illegal for drug companies to market drugs to treat unapproved conditions.

Gabapentin is a commonly used drug

Gabapentin remains a widespread and popular drug.

In 2016, it was the in the United States, with 64 million prescriptions.

As use of a drug grows, so does the unpredictability of side effects and potential for misuse.

“Once released as an approved drug, the number of people being prescribed the drug jumps substantially (tens of thousands to millions), and there is much more variability in the patient population and less control on how the drug is actually being taken,” said Bilsky.

found that gabapentin misuse was low among the general population at just 1 percent. But that jumped to between 15 and 22 percent among people who misuse opioids.

“With decreasing availability of commonly abused prescription opioids, it has been suggested that nonmedical users of prescription opioids are substituting other licit and illicit drugs for abuse,” wrote the authors of a on gabapentin misuse.

Gabapentin isn’t the only “safe” painkiller to show up on the radar of doctors and lawmakers in recent months, either.

As Healthline previously reported, Imodium — an over-the-counter anti-diarrheal drug — has also seen a surge in misuse. So much so that the U.S. Food and Drug Administration announced a plan to help cut down on its misuse potential.

Neither gabapentin nor Imodium is particularly good at getting you high, so reasons for misuse are likely associated with cost and availability.

“It is hard to say what drives the person who suffers from a substance use disorder to switch between drugs and drug classes,” said Bilsky. “The current misuse of gabapentin may be another version of combining drugs to try and maximize the high.”