Workers are using bleach in a bid to beat drug tests at Bay of Plenty businesses.
Latest figures from the New Zealand Drug Detection Agency reveal the number of workplace tests in the region has more than doubled in the last year.
There were 4458 in 2011, compared with 1711 in 2010, with 8.5 per cent positive.
The agency's Bay of Plenty general manager Leigh Sefton said the increase could be down to a rise in testing rather than offending.
He said more companies recognised the benefits of a testing programme, in terms of morale and productivity as well as safety.
Mr Sefton said up to 10 people a week were trying to cheat the tests - with most relying on a friend to provide a clean sample.
"This is usually concealed down the donor's pants in small bottles, condoms or similar receptacles."
Mr Sefton said the level of cheating depended on the type of industry, but most occurred at pre-employment tests.
"The donor is aware that they have a drug test to complete and they come prepared to try and cheat. In a busy week we may have anywhere from three to 10 cheats."
People also tried adding chemicals such as bleach to urine to try to mask drug use and others took cleansing or flushing pills available at various health stores.
"However we still have a number of people fail the test and get quite upset that the flushing product they purchased hasn't worked."
Testing options included pre-employment, random, post-incident or accident and reasonable cause testing - when an employee was displaying recognised indicators or patterns of drug use.
He said the fact people attempted to cheat workplace drug tests was "a real shame".
"They don't seem to realise, or care, that drug testing is all about providing a safe working environment," he said.
Those caught trying to cheat drug tests were usually fired.
"It is a serious issue when someone is willingly jeopardising safety in the workplace," he said.