When I’d gone to the AIDS Healthcare Foundation clinic near my home in South Beach, I wasn’t intending to take an HIV test—I’d been taking PrEP for months, but knew I was still at risk for other sexually transmitted infections. When I arrived, the woman at the desk in the empty waiting room informed me they didn’t do the full spectrum of STI tests until later that day, but she offered to do a rapid HIV test in the meantime. I agreed. She took my name, my address, my sexual history, and then pricked my finger. We waited a moment in the silent room for the results.

You tested positive, she said.

Then she kicked into gear. Do you have people you can talk to? she asked. Yes, I said. A support network? Yes, I said. After arranging a lunch date the following day with one of their counselors, I exited the clinic into the street.

Miami is very sunny in August. It’s not a forgiving place to be sad.

* * *

Truvada, made by the pharmaceutical company Gilead Sciences, was approved by the Food and Drug Administration in 2012 to prevent HIV in those at high risk for infection. Early studies found it to be somewhere between 92 and 99 percent effective. In a study earlier this year of 657 men in San Francisco who took PrEP for two and a half years, it was 100 percent effective; none of them acquired HIV.

The drug is the combination of two chemicals: tenofovir, discovered by Czech and Belgian chemists in in 1984, and emtricitabine, formulated by three Emory University scientists after they attended an international AIDS conference in 1989. Gilead developed an oral form of tenofovir in the late 1990s, and co-bought the rights to emtricitibine from Emory for more than half a billion dollars in 2005. Tenofovir is the bedrock molecule in the company’s four HIV medicines—Truvada, Atripla, Complera, and Stribild—which together comprise a $10-billion HIV franchise.

These medicines aren’t cheap. Truvada can cost as much as $1,500 per month. But even with this profit potential, Gilead has said that it “does not view PrEP as a commercial opportunity,” and only began promoting Truvada as PrEP earlier this year.

And while PrEP is championed by public-health organizations like the Centers for Disease Control and Prevention and the World Health Organization, others in the field approach PrEP with trepidation, concerned it might spur a decline in condom use and fuel an increase in other STIs.

Chief among these is Michael Weinstein, the CEO of the AIDS Healthcare Foundation, who maintains that many gay men won’t take PrEP consistently and that broad use of the drug could spark drug resistance in HIV-positive patients. Last year, Weinstein called PrEP a “party drug” that was a “public-health disaster in the making.”

“If something comes along that’s better than condoms, I’m all for it, but Truvada is not that,” Weinstein told the Associated Press in a 2014 interview.