Some researchers call it a miracle drug: one blue pill that can dramatically reduce the risk of contracting HIV if taken every day as prescribed.

But one year after pre-exposure prophylaxis, or PrEP, was approved by Health Canada, Toronto Public Health is concerned the drug provides a false sense of invincibility for some users that could contribute to the city's rising rates for other sexually transmitted infections.

"People on PrEP … could be more likely to acquire STIs because they may not be using condoms," Dr. Rita Shahin, Toronto's associate medical officer of health, told CBC News. "Once the risk of HIV is eliminated, people may be less likely to use condoms."

Research into the relation between PrEP, STIs and condom use is still very new, and no definitive causal links have been established.

Dr. Rita Shahin, Toronto's associate medical officer of health, says she hopes the city's safe sex advertising on hookup apps will have an impact. (CBC News)

PrEP is sold by pharmaceutical giant Gilead under the brand name Truvada. It's prescribed mostly to gay and bisexual men who are considered at high risk of contracting HIV.

Pharmacist Michael Fanous says that in Toronto's gay community, everybody knows somebody on PrEP.

He has hundreds of clients taking the drug, including sex workers and even a customer in Nunavut who gets his medication shipped by plane.

Toronto pharmacist Michael Fanous says he has hundreds of clients taking PrEP, including sex workers and even a customer in Nunavut who gets his medication shipped by plane. (CBC News)

Fanous himself takes the pill every day.

"Nobody can know with certainty if their significant other, whether male or female, has any other sexual partners," he said.

But he rejects the idea that the advent of PrEP has coincided with an increase in sex without condoms.

"It was already on the rise anyway because we have a new generation that didn't live through the AIDS crisis, who don't know about lifelong infection or fearing acquiring a lifelong infection such as hepatitis or HIV," he said.

"There is no causation or causality between PrEP use and condomless sex and the increase in the STIs."

No 'cure-all'

CBC News spoke with men in Toronto's gay village, and most said they felt safer thanks to PrEP. But some said they're concerned that without the threat of HIV, condomless sex is becoming more popular.

Matthew Young says he took PrEP for one year as part of a clinical trial in Toronto. (CBC News)

Matthew Young said he definitely felt "a little bit more free" when he started taking the drug.

He took PrEP for one year as part of a clinical trial in Toronto and says some men will "assume that [they're] immune to other things, if [they're] not well-educated."

John Carpenter said he sees changing attitudes online, with some PrEP users behaving like they are "invulnerable."

You're putting a lot of trust in someone you're just meeting on Grindr or Scruff, and that can often be misplaced. - John Carpenter

"I do know that a lot of people attempt to use it [PrEP] as some sort of cure-all, and it's not that," said Carpenter, who lives in Toronto with his husband.

"You're putting a lot of trust in someone you're just meeting on Grindr or Scruff, and that can often be misplaced."

A look at interactions and profiles on those and other hookup apps reveals many men are now seeking "raw" or "bareback" sex, explicitly saying it's safe because they're on PrEP.

Raising awareness

Although concerned by this behaviour, Toronto Public Health says that after only a year of tracking the effect of PrEP, "it is very hard to say with certainty if there is any impact yet" on the city's infection rates.

"We have done some advertising on these apps to raise awareness ... about syphilis, in particular, and hopefully, that will have some impact," said Shahin.

According to a report issued last year by the health agency, nearly 90 per cent of all syphilis cases in the city involve men having sex with men.

Data compiled by Toronto Public Health shows that in the nine months after PrEP was approved, reported cases of syphilis did go up seven per cent compared to the same period in 2015, rising from 534 to 573 confirmed cases. Gonorrhea infections went up almost as much in that time.

The same data set also indicates that the number of HIV cases remained stable, declining slightly from 338 to 335. A link between increased PrEP use and this trend is also difficult to establish, as better treatment options for HIV-positive patients could also be a factor.

The agency says these numbers are preliminary and could change as cases are investigated. The data doesn't specify what proportion of syphilis and HIV infections occurred in​ PrEP users.

But the health agency does say the popularity of anonymous hookups with apps such as Grindr and Scruff combined with the declining use of condoms is playing an important role in the "significant hike" in sexually transmitted infections observed in many North American cities, including Montreal, New York and San Francisco.

Toronto Public Health isn't the only agency monitoring this closely.

A 2015 report by the U.S. Centers for Disease Control and Prevention (CDC) noted a "troubling rise in syphilis infections" as well as a growing trend of men having unprotected sex with men.

CDC data shows that since the U.S. Food and Drug Administration approved PrEP in 2012, gonorrhea cases reported in the general population in San Francisco jumped 80 per cent while syphilis cases in New York increased by 52 per cent. In New York, health department officials attributed much of the increase to men having unprotected sex with men.

However, the U.S. numbers did not specify what proportion of those infections occurred in people taking PrEP.

More screening means more cases

Dr. Darrell Tan, an infectious disease specialist at St. Michael's Hospital in Toronto, points out that sexually transmitted infection rates have been rising in the general population long before PrEP was approved in Canada.

A 2013 report from the Public Health Agency of Canada found that rates of chlamydia, gonorrhea and syphilis have been steadily rising since the late 1990s. In Toronto between 2010 and 2016, those three infections saw increases of 31 per cent, 72 per cent and 52 per cent, respectively, according to data from the city's public health agency. Cases of HIV, meanwhile, decreased by 13 per cent in those six years.

Tan led a one-year clinical trial of 52 men in Toronto looking at the impact of PrEP on sexual behaviour and safe sex, the results of which are still pending. He said that so far, no trial or study has been able to establish a clear causal link between PrEP, condom use and STI rates in Canada.

Dr. Darrell Tan, an infectious disease specialist at St. Michael's Hospital in Toronto, led a clinical trial on the impact of PrEP. (CBC News)

However, he says one possible explanation for the rise in reported sexually transmitted infections is more frequent monitoring.

"Patients on PrEP are screened more often than the average patient," Tan said. "They must submit to blood tests and STI screenings every three months to see how their body is responding to the drug."

Fanous, too, thinks it's that rigorous testing that has led to the rise in reported STIs.

"If we take PrEP away from the equation, and we just tested men every three months anyway for STIs — men and women — we would've seen more positive test results," he said.

Fanous and Tan both see the close monitoring that PrEP users undergo as something positive.

Tan says that in the long run, the repeated screening could actually lower infection rates.

If doctors spend more time testing and helping high-risk patients, he says, infections can be treated faster, which can stop further spread and eventually lead to healthier populations.