Welfare recipients targeted in the government’s controversial drug-testing trial will be forced to disclose their prescription medications to a third-party contractor to minimise false positives, documents obtained by Crikey reveal.

Centrelink clients will be quizzed on their medications by an as yet unannounced tester after the Department of Social Services flagged the possibility of prescription drugs interfering with tests for illicit substances, internal policy documents show.

The documents, obtained under freedom of information laws, acknowledge that the “majority of drug tests have a rate of false positives,” requiring the “drug testing provider to account for any legal medications that may cause a false positive.”

The Department of Human Services intends to outsource its planned drug testing of welfare recipients to a private company, but it has yet to announce the winning bidder.

The policy materials, compiled by the department to answer likely objections raised against the testing scheme, further state that those tested “may be required to provide evidence” of their prescription medication.

Legal medications that could potentially trigger a false positive result include painkillers such as Nurofen Plus and amphetamine-based medications such as dexamphetamine and Ritalin, according to Dr Ken Pidd, deputy director of the National Centre for Education and Training on Addiction.

“For most onsite screening devices these medications will not be distinguishable from illicit drug use, however the subsequent laboratory analysis will be able to identify them as prescribed/OTC drugs,” Pidd told Crikey. “So there may be an issue if the welfare recipient does not declare the use of these drugs prior to the onsite test and this may occur if the welfare recipient has low literacy levels, poor English skills, or impaired communication ability.”

In May, the Turnbull government announced that it would drug test 5000 recipients of Newstart and Youth Allowance from January, ad those who tested positive would have their benefits cut or moved onto card-based cashless payments.

The Prime Minister has described the policy as motivated by “love” and has attempted to justify it on the grounds it prevents taxpayers from inadvertently funding drug addictions. But rehab workers and anti-poverty campaigners have slammed the move as stigmatising and discriminatory.

[Destroying the joint: drug testing welfare recipients will be expensive and won’t work]

The revelation that welfare recipients will be compelled to reveal sensitive medical information to a private firm, however, raises new privacy questions at a time of heightened scrutiny of the government’s handling of personal data.

Earlier this month, The Guardian revealed that Medicare details were freely available for purchase on the “dark web” for as little as $20. In May, ATO Commissioner Chris Jordan revealed that some 30 employees had been caught improperly accessing taxpayer information so far this year, not including several staff under investigation in connection with the Plutus Payroll scandal.

Centrelink itself was embroiled in controversy in February when government bureaucrats shared information about a blogger’s welfare history with a journalist to counter her negative portrayal of its beleaguered debt-recovery program.

“The requirement for welfare recipients to have to ‘assist’ Centrelink and its contractors by providing information about their medical history and current medications represents an unnecessary intrusion into their privacy and right to confidentiality in their relationship with medical professionals,” Greg Barns, spokesman for the Australian Lawyers Alliance, told Crikey.

Barns, a longtime privacy advocate, raised concerns about how the department might use medical information that came into its possession.

“For example, Centrelink might seek to investigate why a person is taking this medication or build a profile of that person based on their medication use,” he said. “There is also the issue of the leakage of this information to other agencies or to third parties. Centrelink has a poor track record of information security and the capacity for data leakage about an individual’s health needs is real.”

A DSS spokesperson rebuffed questions from Crikey, saying the government would make further announcements about the trial at an appropriate time.