Figures showing more women are in jail because of methamphetamine-related offences highlight the need for drug treatment in prisons, a reform group says.
The number of female inmates has almost doubled, to about 500, in the past five years.
Corrections Minister Judith Collins says 11% of women imprisoned during the past financial year were convicted of methamphetamine offences.
The president of the Howard League for Penal Reform, Peter Williams, QC, says Wellington's Arohata Prison is the only jail offering women an effective drug treatment programme.
But he says many do not want to transfer there from other jails, because their families could not afford to visit.
"As a consequence of that, a lot of women who otherwise would be in Arohata and would be getting some sort of treatment for addiction are just not there."
Mr Williams believes female remand prisoners should also get drug treatment.