The Queensland ombudsman has found women inmates at a Townsville jail were unlawfully strip searched for nearly a year.

Female inmates were unlawfully and unreasonably strip-searched because they were taking controlled medication, the Queensland ombudsman says.

The Townsville Women’s Correctional Centre began conducting strip searches in June 2013 after becoming suspicious that some prisoners were “diverting” their medication.

The class of substance, which includes codeine, oxycodone, methadone and morphine, is controlled under state and federal law due to its potential for abuse.

Guards suspected inmates were using methods such as cigarette filters in their mouths to soak up the drug for future use.

At least 18 women were strip-searched, both before and after taking their medicine, over a 10 month period.

One woman occasionally took medication three times a day, which meant she was subjected to six searches daily.

The practice was dropped in early 2014 after a complaint.

In a report tabled in Queensland parliament on Tuesday, ombudsman Phil Clarke said there was a lack of documentation about the practice.

“The investigation revealed that the practice was both unreasonable and contrary to law,” Mr Clarke wrote.

The ombudsman received allegations that staff were conducting searches “in a way that failed to appropriately safeguard prisoners’ dignity”.

Prisoners who were interviewed said the searches were a negative experience.

“One prisoner reported that she found the practice demeaning and she came away from it feeling like she had been sexually abused, bringing back memories of her own past abuse,” the report said.

No other correctional centre in the state was routinely strip-searching inmates who were taking controlled medications.

Mr Clarke praised the Queensland Corrective Services director-general for acting swiftly to address the issues raised in the report.

But he said it was concerning that the department’s oversight mechanisms had failed to identify an unlawful and unreasonable practice that had occurred for so long.

Mr Clarke recommended refresher training for the centre’s officers and the proper documentation of orders to strip search inmates.

The department’s oversight mechanisms should also be reviewed, Mr Clarke said.