The drugs used in PrEP are already licensed for use as part of treatment for HIV-positive people. Although the European Medicines Agency has not yet licensed the drugs for use in HIV prevention, doctors are able to prescribe the drugs outside the terms of the licence. This is known as ‘off-label’ use and is already regularly practised for post-exposure prophylaxis (PEP).

PrEP has been available in the United States since 2012 but uptake was initially slow. Barriers have included lack of awareness among people at risk, concerns about side-effects, the stigmatisation of PrEP users, resistance from some medical providers, inconsistent insurance coverage and services not being geared up to provide it. During 2014 and 2015, increased advocacy and media coverage of PrEP have contributed to greater use, especially in San Francisco. In 2014, 16% of people attending the city’s main sexual health clinic were taking PrEP and 60% wanted to.

So far, there is no evidence of the ‘worried well’ seeking out PrEP. People with riskier sexual behaviour and recent sexually transmitted infections seem to be more likely to choose to take PrEP and to have high levels of adherence.

PrEP has been controversial in the United States, with some people stigmatising PrEP users as irresponsible barebackers. Others have framed PrEP as a responsible and pro-active way to protect their health.