Corrections Minister Judith Collins says the number of prisoners testing positive in random drug tests has reached an all-time low.

She says that in the year to 31 December 2015 there were over 4500 random drug tests on prisoners. The rate of positive results was 3.1%. This compares to a positive result rate of 10% in 2009/10 and 22% in 2000/01.

Ms Collins says all prisoners are screened for alcohol and drug problems when they enter prison to determine support required.

She says two thirds of prisoners enter prison with drug and alcohol problems. Drug and alcohol treatment is available in prison.