Facebook users have been bombarded with misleading ads about medication meant to prevent the transmission of HIV, according to lesbian, gay, bisexual and transgender advocates, who say the tech giant’s refusal to remove the content has created a public-health crisis. The ads have been viewed millions of times in recent months, Facebook’s archive reveals, and LGBT organizations argue they’ve had a dire effect: They’ve scared patients, potentially those who may be most at risk of contracting HIV, out of taking preventative drugs, known as PrEP, even though health officials and federal regulators have said they are safe. Many of the ads appear to have been purchased by personal-injury lawyers and entities affiliated with them. They allege in lawsuits that HIV medications, such as Truvada, actually threaten patients with serious side effects. But groups led by GLAAD, which regularly advises Facebook on LGBT issues, say the ads are “false” and have urged Facebook for months to take them down — to no avail.