The findings were announced at a press conference attended by Dr Kajit Chupanya, a former deputy Bangkok city clerk who heads the research project, and US Ambassador Kristie Kenney.
Kajit said the risk of HIV infections dropped by 74 per cent among those taking tenofovir every day.
“This is the first evidence of pre-exposure prophylaxis among injecting drug users,” he said. The findings from the research project were published in the online medical journal the Lancet.