Why is it possible – and so easy – for people to buy illicit drugs like Oxycontin on Facebook? This is one line of questioning that Mark Zuckerburg has faced during his time being questioned by the House as well as the Senate.

West Virginia Republican David McKinley told Mark Zuckerberg his platform is hurting people, as he shared a screenshot of an ad on Facebook looking to sell opioid pills. He said that the ad has been on the platform since last September.

“America is in the midst of one of the worst epidemics that it’s ever experienced with this drug epidemic. It’s all across this country but you’re platform is still being used to circumvent the law and allow people to buy highly addictive drugs without a prescription. With all due respect, Facebook is actually enabling an illegal activity and in so doing, you are hurting people,” Rep. McKinley said. “When are you going to take down these posts?”

Zuckerberg told the committee that it’s impossible to police every piece of content on the website, but he is working on using artificial intelligence that can flag material for review. Yesterday, in the Senate, a few Congresspeople alluded to CNBC’s report in 2017 that Facebook is a place where you can find uncensored postings from drug dealers from both the US and overseas touting oxycodone and other dangerous opioids.

CNBC found dozens of ads illegally selling drugs on the Facebook platform, yet many of them remained although they contacted Facebook and reported the postings. Even after Facebook sent notice that they would be taking action, the ads stayed on the website for several days.

The information on opioid sales on Facebook is especially troubling considering that Mark Zuckerberg has spoken about how the scope of the opioid crisis had been startling and concerned him as a public health issue. He’d been able to witness it firsthand during a speaking tour in the some hardest-hit states.

“One thing we don’t fully internalize, how this epidemic has affected people’s attitudes more broadly…it’s one of the worst public health issues,” he said in a live stream last November. Mr. Zuckerburg also has spoken of a desire to run for office, but it would be hard to gain credibility on the crisis without cleaning his own house, first.

The House panel on Facebook’s data leak continues through the end of today.