NSW Premier Gladys Berejiklian says she is "convinced" a government inquiry into amphetamine use will find no evidence to support pill testing.

With the inquiry's first public hearings due to begin in Sydney next week, Ms Berejiklian said it was important for Commissioner Dan Howard SC and his 16-member expert panel to undertake a "robust independent approach" to the issues.

Premier Gladys Berejiklian, with Health Minister Brad Hazzard and NSW Police Commissioner Mick Fuller, as she announced the special commission of inquiry into ice in November 2018. Credit:AAP

But the Premier said her opposition to pill testing remained "firm" and she was confident the panel would not find evidence to support recommending a pill testing trial.

"I'm convinced there is no evidence to support pill testing, but it's important for the Commissioner and his experts to have a free reign to look at these issues and provide their recommendations," Ms Berejiklian said on Tuesday.