Facebook has quietly started removing some misleading ads about HIV prevention medication, responding to a deluge of activists, health experts and government regulators who said the tech giant had created the conditions for a public-health crisis.

The ads at issue — purchased by pages affiliated with personal-injury lawyers and seen millions of times — linked drugs designed to stop the spread of HIV with severe bone and kidney damage. Lesbian, gay, bisexual and transgender advocates long have said such claims are “false,” pointing to multiple studies showing the class of medication, known as PrEP, is safe.

After initially declining to disable the ads, Facebook began on Friday retroactively labeling some of them as rule violations in its archive, limiting their visibility. The company’s third-party fact-checkers concluded the ads were misleading and lacked context, according to a copy of an email sent by those fact-checkers to LGBT groups that was shared with The Washington Post, which first reported on the matter earlier this month.

The change in course at Facebook drew praise from LGBT organizations that had worked since September to stop the spread of HIV misinformation on the social media platform. But many activists said they remain uneasy that it took so long to get Facebook’s attention in the first place — and worried the company’s policy on such ads in the future remains unclear.

“The removal of select ads is a strong first step given the findings of Facebook’s own fact-checking agency and the dozens of organizations that spoke out," said Sarah Kate Ellis, the leader of GLAAD. She added the “time is now for Facebook to take action on other very similar ads which target at-risk community members with misleading and inaccurate claims about PrEP and HIV prevention.”

Facebook spokeswoman Devon Kearns confirmed that the company had taken action against some of the ads. “After a review, our independent fact-checking partners have determined some of the ads in question mislead people about the effects of Truvada," she said, referring to the name of the drug. "As a result we have rejected these ads and they can no longer run on Facebook.”

The incident illustrates Facebook’s persistent struggle to police its service, which reaches 2 billion people globally, and prevent the real-time spread of harmful posts, photos, ads and other troubling content.

Facebook has tapped thousands of human reviewers, invested in artificial intelligence and repeatedly revised its rules on what it allows and what it removes, particularly with an eye to preventing trouble during the 2020 presidential election.

But its decisions often have left users, including regulators, deeply dissatisfied, feeling as though the company isn’t acting swiftly or aggressively enough to thwart online abuse, including misinformation that has the potential to result in real-world harm. In fact, many of the controversial ads about HIV prevention medication, purchased by Facebook pages associated with lawyers suing the drugs’ manufacturers on behalf of people who say they were harmed by the medication, had stopped running by the time Facebook took action against them last week.

LGBT activists, led by GLAAD, started trying to get Facebook’s attention about the issue more than three months ago. They formally asked one of its fact-checking partners, a non-for-profit called Science Feedback, to review the ads in November, according to Jessica P. Johnson, its science editor. Facebook asked for a review on Dec. 13, she added, four days after The Post published its initial story and LGBT groups went public with their concerns.

The problem with the ads, LGBT advocates argued, is that they conflated the two applications of HIV-related drugs when, in fact, the preventive form, or PrEP, is safe. The advocates pointed to medical experts, including the Centers for Disease Control and Prevention, which publicly advises PrEP is “highly effective” and “recommended” for people at high risk. Absent swift action, organizations including GLAAD, the Human Rights Campaign and the Trevor Project said the ads threatened to scare patients away from a critical drug.

Facebook initially declined to take them down, signaling it would wait for a decision from its third-party fact checkers. Its handling of the issue drew sharp rebukes from top government officials, including New York Gov. Andrew M. Cuomo (D) and Sen. Elizabeth Warren (D-Mass.), who is seeking her party’s nomination for president. Warren, who also has been critical of Facebook’ policies on political ads, said Facebook’s inaction could “have serious public health consequences,” adding in a tweet: “Facebook needs to put the safety of its users above its own advertising profits.”

Sen. Robert Menendez (D-N.J.) also penned a letter to the tech giant, demanding answers in response to The Post’s reporting. Menendez blasted the company in his Dec. 20 letter for exhibiting “complacency” and potentially putting “advertising profits over Americans’ lives.”

Months after LGBT groups first sounded the alarm, Facebook’s third-party fact-checkers responded on Friday: They agreed the ads’ claim about PrEP was “misleading,” explaining in some cases it “overstates the risks for those who take Truvada as a preventive rather than as a treatment.” Science Feedback told LGBT activists that Facebook “has decided to begin marking this and similar ads as containing false or misleading information.”

In response, Facebook disabled a series of ads, some of which had already ceased running on its service. But it did not ban all ads about drug-related lawsuits, or HIV prevention medication, nor did it issue any new policies around those who pay to reach users on those topics.

Some ads linking bone and kidney damage to PrEP also remained fully visible in Facebook’s public ad archive, raising questions as to how exactly the company would apply its rules in the future. The company, for its part, says it’s still reviewing ads related to the medication.

“It’s gratifying to see one of Facebook’s fact-checkers back up the overwhelming consensus of AIDS, LGBTQ, and HIV medical groups that these ads are misleading," said Peter Staley, a co-founder of the PrEP4All Collaboration who previously raised some of the troubling ads with Facebook.

“But Facebook has put a warning on only one ad thus far, with many more unaffected,” he continued, adding: “If this is their official response, after ignoring us for months, then it’s a mess.”