A new HIV prevention drug, pre-exposure prophylaxis, will be trialled in South Australia, the state government says.

The South Australian government will fund the trial of a drug that can help prevent people contracting HIV.

Pre-exposure prophylaxis, or PrEP, will be made available to people who don't currently have the virus but are considered at high risk. It involves taking a single pill each day.

Premier Jay Weatherill says the trial will provide South Australians living at risk of contracting HIV with access to an additional, effective prevention method.

The government believes about 500 people will be eligible to take part in the trial.

It is estimated that for every 13 people on PrEP, one HIV infection is averted but it's success rate can be much higher in some target groups.

In May this year the Therapeutic Goods Administration approved the drug for supply in Australian but an application to list it on the Pharmaceutical Benefits Scheme was rejected in August.

The SA government has accused the commonwealth of being slow to act but the SA opposition says the state government has also been dragging the chain.

It says other states are already running trials with about 8000 people taking part.