(NewsNation) — The U.S. continues to battle a crisis as fentanyl flows into the U.S., mainly across the southern border, resulting in deadly overdoses.

Stanford Psychiatry and Behavioral Sciences professor Keith Humphreys joined NewsNation to discuss how fentanyl surpassed other opioids to become the biggest drug problem the country is facing.

Humphreys said the rise in fentanyl was driven by suppliers who move drugs into the U.S., not by people using drugs.

“It’s not that people demanded it, it’s that it is synthetic. It does not require agriculture, it does not require long supply lines. So the profit margin for traffickers is much higher. And that’s why they went into it,” he said.

That also means drug traffickers are unlikely to stop moving fentanyl into the U.S. There are already reports of fentanyl being increasingly mixed with other drugs, potentially leading to overdoses in people who don’t even realize they’re ingesting something so strong.

Humphreys said a focus on treatment is critical because it won’t be possible to completely eliminate the supply of fentanyl, even if officials manage to reduce the amount of the drug being smuggled into the U.S.

“That’s why prevention and demand reduction, meaning you know, helping people get into treatment and get into recovery, who have a problem already, is always going to be a critical part of responding to drugs in the United States,” he said.

That includes investment in resources to treat substance use disorders, Humphreys said, adding that he hopes the new Congress will listen to constituents who are seeing the toll fentanyl takes on their communities and want change.

“It’s definitely like other chronic illnesses. Addiction does require resources in the health care system,” Humphreys said.