Rating 21 of 44 prisons as over capacity, the Inspector of Custodial Services, John Paget, has said NSW had forgotten what a prison riot looks like, or its cost and consequences.

With staff and inmates under "significant stress", Mr Paget noted the looming smoking ban, and warned: "Even small additional pressures can make the difference between conditions that are uncomfortable and those that are intolerable."

It is estimated 80 per cent of prisoners smoke.

The President of the Australian Drug Law Reform Foundation, Alex Wodak​, said he was fervently anti-smoking, but opposed an enforced ban in prison because it wouldn't work.

Overseas experience had shown banning cigarettes only drove up their price and created a black market, which became a gateway for other drugs, he said.

"No research tells us that if you force people to stop smoking in prison they will stay stopped after they are released. There is a lot of evidence of significant harm."

He said smoking bans introduced recently to prisons in Queensland and Tasmania had increased tension and led to riots.

The ABC reported in April that Tasmanian prisoners smashed accommodation and microwave ovens, after smoking was banned in February.

Prisoners had mixed nicotine patches with tea leaves to create substitute cigarettes, until tea bags were also removed from Hobart's Risdon Prison.

In Queensland, prisoners protested on rooftops.

"We should instead be offering prisoners and staff the choice to reside in a smoking or non- smoking wing," Dr Wodak said.

Justice Action spokesman Brett Collins said the ban was "a shocker" and would lead to anger and resentment among NSW prisoners.

"Its an extremely traumatic thing to have cigarettes removed involuntarily. It's the one personal thing they control," he said.

For prisoners to quit smoking permanently, like anyone else in the community, they have to make the decision and "own the change themselves", he said.

Mr Collins said he was told in a meeting last week by Corrective Services Assistant Commissioner Luke Grant the smoking ban wasn't about prisoner health, but occupational health and safety for staff.

Monash University's Anita Mackay, who researches human rights in prisons, said smoking bans in Australian prisons were new, but the experience overseas showed such bans only drove smoking underground, with non-smokers unable to complain because it would breach the prisoners' code of "you don't dob people in".

"The real problems are overcrowding, and prisoners in Australia spending their time in their cells. If people spent the day outside cells you could set up smoking rooms," she said.

Corrective Services Minister David Elliott, appointed in April, said NSW prisons would be smoke-free from August, despite Mr Paget's warning.

"A range of services will be available for staff and inmates to support them to stop smoking, including Nicotine Replacement Therapy, peer and telephone support such as Quitline and counselling services," he said.

Mr Collins responded: "Anyone who has struggled with patches in the community knows they create tension."

Prisoners in NSW spend 16 hours a day in shared cells, and have the shortest period out of cells of any state. They are locked down from 2.30pm because of staff shortages.

Mr Paget's report was concerned there is a one month wait to see a doctor.

Prisons were exempted from minimum floor space requirements in the NSW Public Health Act in August to allow centres to squeeze three prisoners into cells designed for one or two people.

"When the state treats inmates in a way that denies them a modicum of dignity and humanity it should not be surprised if they respond accordingly, with individual acts of non-compliant behaviour escalating into collective disorder, such as riots," Mr Paget wrote.

Mr Elliott said he would seriously consider Mr Paget's recommendations.