A Mosgiel woman visiting a prisoner at the Otago Correctional Facility at Milburn was arrested when drugs were discovered in the car she was driving, which belonged to a friend.
The car passed through a prison checkpoint, which was set up on the road leading to the facility, and a small amount of cannabis was found mixed with some tobacco in a tobacco pouch, along with "point bags" that contained BZP residue.
The woman was detained at the prison before being arrested by Balclutha police.
Constable Judy Powell said the woman was trespassed from the prison, but not charged, because the amount of drugs in question was so small.
The owner of the car received a warning from police.
"People need to be aware that you are subject to being searched when you are on prison property."
It had a knock-on effect, and being trespassed meant people would not be able to visit their family members in prison, Const Powell said.
Otago Correctional Facility manager Jack Harrison said demand for drugs in prisons was high.
"Unfortunately, prisoners put a lot of pressure on their friends and family to smuggle it in for them.
"It is unacceptable, and the exact reason why we continue to be vigilant in our search and our general screening of visitors, contractors and staff."
He said every person who entered a prison went through the same security process.
"We will not hesitate in taking action against people naive enough to think that they will get away with it," Mr Harrison said.
