On a brilliant blue California morning, an ambulance idles up San Francisco’s Castro Street. A small rainbow flag flutters from its antenna while its speakers blare:

Young man, there’s no need to feel down!

Two days before one of the largest Gay Pride parades in the US, nearly everything in sight has been decked with rainbow flags. And balloons. And bunting.

Men young and old have begun streaming into the city’s largest sexual health clinic, Magnet at Strut, while a free consultation service at the University of California at San Francisco about two miles east is being swamped with calls from healthcare providers around the Bay Area. Many are desperate to get their patients started on the same blue pill before the weekend’s festivities lead to a flurry of hook-ups.

It’s not the little blue pill you might be thinking of. It’s Truvada, the brand name of a daily HIV prevention pill known as pre-exposure prophylaxis, or PrEP. The two-drug combination was originally formulated as a virus-suppressing therapy for HIV-positive people, but clinical trials later suggested it was also effective at blocking the virus from taking hold in the first place. In 2012 the US Food and Drug Administration gave it additional approval as a preventive drug, further expanding its use in May 2018 to include at-risk adolescents.

After a slow start, Truvada is surging in popularity around the world among men who have sex with men. Although good numbers are lacking, San Francisco is widely believed to have the highest uptake in the world. There, the rate of new HIV infections roughly halved between 2012 and 2016, attributed largely to more testing, better use of treatment to make people with HIV uninfectious, and PrEP.

In city after city, public health officials and doctors have begun crediting PrEP with helping to dramatically reduce HIV transmission rates. In New York, Chicago, London, Sydney, Melbourne. All this is in spite of some formidable barriers to access and an ongoing backlash – especially from other gay and bisexual men.

PrEP is a “party drug” for people who want to have riskier sex but who can’t be expected to take the pills responsibly, critics have said.

It is a “boutique intervention” that will only be used by the few.

It will lead to more drug-resistant HIV.

It will cause “complacent” men to abandon condoms en masse and drive up rates of other STIs.

It will lead to more antibiotic-resistant gonorrhoea and could contribute to syphilis and other infections following suit.

In 2012, HIV campaigner and writer David Duran coined the phrase “Truvada whore”, to blast PrEP as a gateway to “unsafe practices” by other gay men and as a likely contributor to the spread of other STIs. In their defiant response, PrEP supporters began wearing “Truvada whore” T-shirts. Writing since, Duran says his “slut-shaming” and “ignorant” attitudes have shifted and he now embraces the prevention strategy. But the assumption that PrEP has encouraged gay and bisexual men to forgo condoms and fuel the recent surge in other STIs has nevertheless become so widespread that a recent op-ed in the New York Times questioned whether the pill’s arrival heralded “the end of safe gay sex”.

Even gay publications have called the rise in other STIs PrEP’s “nasty downside”, while researchers have lamented a “failure” in safer sex messaging.

What if this common narrative isn’t quite right? Read more via Mosaic