HIV transmissions are at historically low rates amongst high-risk men on prevention medication in NSW.

HIV transmissions in NSW dropped 40 per cent when prevention medication was made more easily available and these historically-low rates have been sustained among high-risk men, a study reveals.

The research, published in The Lancet HIV on Friday, is the culmination of a three-year study called EPIC-NSW, the first globally to measure the impact of pre-exposure prophylaxis (PrEP) on reducing HIV in a large population.

The Kirby Institute's Professor Andrew Grulich, who led the study at the University of NSW, said the "modest cost" of accessing PrEP once it was subsidised through the Pharmaceutical Benefits Scheme in 2018 did not lead to higher HIV transmission among the almost 10,000 gay and bisexual men who participated.

The medication was dispensed for free as part of the trial, which began in 2016, but is now available for about $40 a month on the PBS.

"For the year following its listing on the PBS, we found PrEP use remained high among the study participants, and HIV rates remained very low, at about two in 1000 participants per year," Prof Grulich said.

The study showed that although HIV rates were low, they were slightly higher in four groups: men aged under 25, men living outside of the gay areas of inner Sydney, men who reported more risk behaviours, and men who stopped taking PrEP.

Prof Grulich said everyone at risk of HIV should have access to PrEP regardless of their residency status.

He echoed calls made a fortnight earlier by the Australian Federation of AIDS Organisations which called on the federal government to invest an additional $53 million to expedite approval and funding of testing and medicines to stop the epidemic from reaching its sixth decade in Australia.

EPIC-NSW was originally designed to monitor the impact of PrEP on HIV rates among 3700 HIV-negative people in NSW for one year, but due to demand early on, it was expanded to anyone in NSW who was eligible.

The study tripled in size and duration, ultimately enrolling 9709 people and regularly testing them over three years.