Treating HIV-infected people with antiretrovirals can "significantly reduce" the transmission rate between partners.
This is according to recent research sponsored by the National Institute of Allergy and Infectious Diseases.
According to the clinical trial, taking oral antiretroviral medicines when infected people's immune systems were relatively healthy reduced the risk of transmitting the virus to their sexual partners.
Director of the institute, Anthony Fauci, commented: "Previous data about the potential value of antiretrovirals in making HIV-infected individuals less infectious to their sexual partners came largely from observational and epidemiological studies.
"This new finding convincingly demonstrates that treating the infected individual - and doing so sooner rather than later - can have a major impact on reducing HIV transmission."
A total of 1,763 couples were involved in the study, all of whom were aged at least 18.
However, they were 97 per cent heterosexual, which, the researchers explained, precludes any definitive conclusions about the effectiveness of the drugs in men who have sex with men.