A new daily pill could dramatically reduce the risk of infection for people suffering from HIV. British researchers were astonished to see an 86 percent reduction in rates of infection among participants. US researchers saw a 92 percent drop.

The drug is called Truvada and is manufactured by Gilead. It has just been approved in the US for pre-exposure prophylaxis (PrEP). The drug is currently awaiting approval in the UK.

The UK trial took place in 13 sexual health clinics over the course of a year. The results, published in the Lancet, found that for every man who took PrEP, 13 new cases of HIV could be prevented.

In the US study, 657 people in the San Francisco Bay area were given Truvada. No new cases of HIV were reported in the area.

However, some caution is in order. In both cases, participants returned with new sexually transmitted infections other than HIV- as many as half in the US study.

“The data say that people don’t necessarily increase their risky behaviors and they don’t decrease their risk in this kind of setting either,” said Dr. Kenneth Mayer, the founder, co-Chair and medical research director of The Fenway Institute in Boston.

Part of this may have been because, while taking PrEP, patients visit the doctor more, making the new infections more readily found than they would have been otherwise.

Yet, 41 percent of participants also reported that they were less likely to use a condom while using PrEP.

“I don’t think PrEP is the magic bullet, but we know that it does work really well,” said study author Dr. Jonathan Volk, an infectious disease physician at Kaiser Permanente San Francisco Medical Center. “It’s great to know we have options.”

Researchers will now move on to see how well PrEP works for other at risk groups such as transgender women.