(NewsNation) — If you ask Tom Wolf, he’ll tell you fentanyl is virtually the only drug now being sold on the streets of San Francisco.

As a former heroin and fentanyl addict, he should know. He spent six months homeless on the streets of San Francisco. He went to rehab in 2018 and has been clean ever since.

Now, he’s become a strong voice speaking out on homelessness and the drug crisis.

He joined “CUOMO” on Thursday to talk about the current drug epidemic in San Francisco.

“Fentanyl has completely changed the game,” he said. “It’s replaced heroin out here on the street, to where you can’t even purchase heroin on the streets of San Francisco anymore. Everything is fentanyl.”

Wolf also explained the basics of a new drug dubbed “ISO,” a new synthetic opioid. NewsNation affiliate KRON-TV reported that city officials are working to monitor and track the emergence of the new drug.

“It costs more so not everybody has gravitated over towards it, but from the people I’ve talked to on the street that have used it, they like it a lot because it keeps them higher for longer,” Wolf said. “If the cartels decide to flood the market with ISO, you’re going to see the price drop way down, and when that happens, we all need to buckle up because this drug is naloxone-resistant.”