The first-ever daily pill to help prevent the spread of HIV has been approved by US regulators - a milestone in the 30-year battle against the virus believed to cause AIDS.
The US Food and Drug Administration on Monday approved Gilead Sciences' pill Truvada as a preventive measure for people who are at high risk of acquiring HIV through sexual activity, such as those who have HIV-infected partners.
Public health advocates said the approval could help slow the spread of HIV, which has held steady at about 50,000 new infections per year for the last 15 years in the US.
Gilead Sciences has marketed Truvada since 2004 as a treatment for people who are already infected with the virus.
But starting in 2010, studies showed that the drug could actually prevent people from contracting HIV when used as a precautionary measure.
A three-year study found that daily doses cut the risk of infection in healthy gay and bisexual men by 42 per cent, when accompanied by condoms and counselling.
Last year another study found that Truvada reduced infection by 75 per cent in heterosexual couples in which one partner was infected with HIV and the other was not.
Because Truvada is on the market to manage HIV, some doctors already prescribe it as a preventive measure.
FDA approval will allow Gilead Sciences to formally market the drug for that use, which could dramatically increase prescribing.
However, the regimen is estimated to cost around $14,000 per year, putting it out of reach for many.
Common side effects of the pill include diarrhoea, nausea, abdominal pain, headaches and weight loss.