Newly-released freedom of information (FOI) documents show nearly 5,000 motorists across New South Wales were charged with drug driving offences between July 2014 and June last year.

Police released the FOI data ranking every postcode in terms of roadside drug testing offences.

The postcode with the highest number of roadside drug test offences was 2580, which includes areas like Goulburn, Mount Fairy and Taralga.

That postcode had 699 offences in the three years to June 2015.

Several Hunter Valley postcodes were also identified as hotspots for drug driving offences.

The postcode 2324, which includes areas like Raymond Terrace and Karuah, was fifth on the list of more than 300 postcodes, with 125 offences.

Postcode 2304, which includes Mayfield and Sandgate, had 68 offences and was 10th, while 2303, which includes Hamilton, was 11th.

Northern region traffic tactician Chief Inspector Trent Le Merton said he was not surprised.

"Our operations basically identify geographic areas that we go to and we do a saturation style operation, where a significant number of people are stopped and tested for both alcohol and drugs," he said.

Despite the figures, Chief Inspector Le Merton said all motorists should be on alert for roadside drug testing, not just those in areas identified as hotspots.

He said while the areas listed were known for such offences, all motorists needed to be aware.

"It's no different to RBT," he said.

"We have stationary operations, we have mobile operations. Depending the mode of operation used, the detection rates vary, but people can expect that at any time they can be tested for alcohol or drugs or both."