Washington DC - Members of Congress on Thursday called on Meta chief Mark Zuckerberg to give them details about ads for opioids and other drugs on the tech giant's platforms.

"Meta appears to have continued to shirk its social responsibility and defy its own community guidelines," a letter singed by 19 lawmakers read.

"What is particularly egregious about this instance is that this was not user generated content on the dark web or on private social media pages, but rather they were advertisements approved and monetized by Meta."

The Tech Transparency Project in March reported finding more than 450 ads on Instagram and Facebook selling an array of illegal drugs.

Many of the ads "made no secret of their intentions," showing photos of prescription drug bottles or bricks of cocaine, and encouraging people to place orders, according to the non-profit research group.

The investigation involved searching Meta's Ad Library for terms including OxyContin, Vicodin, and pure coke, TTP reported.

The letter from Congress members to Zuckerberg asked for answers from Zuckerberg by September 6.

Questions included how may illicit drug ads Meta has run on its platform, what it has done about them, and whether viewers were targeted for such ads based on personal health information.

Meta planned to respond to the letter.

"Drug dealers are criminals who work across platforms and communities, which is why we work with law enforcement to help combat this activity," a Meta spokesperson told AFP.

"Our systems are designed to proactively detect and enforce against violating content, and we reject hundreds of thousands of ads for violating our drug policies."