Two-thirds of people in the state's prisons were using the drug ice before being locked up, a Special Commission of Inquiry into the drug has heard.

Key points: The inquiry heard 11.4 per cent of men first injected drugs in jail or juvenile detention centre

The inquiry heard 11.4 per cent of men first injected drugs in jail or juvenile detention centre Almost 700 prisoners tested positive for drugs in the first six months of this year

Almost 700 prisoners tested positive for drugs in the first six months of this year The inquiry is focusing on adequacy of health services for users in jail and support upon released

The inquiry sitting in Sydney paints a bleak picture of drug use among the state's prison population, with 8,000 active amphetamine users entering custody last year.

Counsel assisting the inquiry Sally Dowling SC said on average 54 people went to jail each day in New South Wales and "on a conservative estimate" at least 22 of those were using ice daily before their incarceration.

Ms Dowling said the inquiry would hear evidence of "the ready availability of drugs in prisons and the prevalence of injecting drug use in custody" and its "serious health impacts".

"The supply of drugs into prisons is without question a very serious problem and one about which the community is entitled to be very concerned," she said.

Hundreds of positive prison drug tests

Ms Dowling today told the inquiry in the past six years to June the prison population had increased by 40 per cent to 13,403 and included "people who have spent their lives on the social and economic fringe of our community".

High numbers of prisoners withdraw in jail, placing staff under pressure. ( Kate Hill : ABC Local )

Almost a quarter of the adult population and almost half of the juvenile population was Aboriginal, the inquiry heard.

It heard 11.4 per cent of men and 2.7 per cent of women had first injected drugs either in jail or a juvenile detention centre.

Thousands of drug tests are performed every year and in the first six months of this year almost 697 prisoners tested positive for ice.

That figure far exceeds the whole of last year, despite the fact that there were fewer drug tests carried out.

The hearing was told "one of the big issues" was how Corrective Services coped with "such high numbers of people withdrawing" and "the risks for inmates and the pressure it puts on staff".

She said there was "no doubt that inmates can access virtually any drug they want if they are prepared to pay the right price".

'Easier to get drugs in jail'

Former ice addict Nicola Tillier started using speed when she was 12, and switched to crystal meth after the State Government introduced limitations on pseudoephedrine sales.

In evidence to the inquiry in May, the 50-year-old, who is now a drug counsellor, said she turned to crime to sustain her habit.

"During the time I spent in jail, I was exposed to a lot of drug use. I believe it is easier to get drugs in jail than it is outside," Ms Tillier told the hearing.

Nicola Tillier says she was exposed to a lot of drugs while in jail. ( AAP: Perry Duffin )

The inquiry on Monday heard it would focus on the adequacy of health services to prisoners who used drugs in jail and the support they received when the re-entered the community.

The inquiry heard prisoners were played a "Health Survival Tips" video, highlighting the importance of cleaning needles before injecting drugs.

But Correctives Services' current harm-reduction policy did not "comply with international best practice".