Barbara Olsen-Henderson tells of the trouble she is having hiring workers who are not using drugs.

A restaurant owner says she has lost count of the number of New Zealanders who have failed drugs tests when applying for a job - while overseas workers have passed every time.

Barbara Olsen-Henderson, owner of the Bach On Breakwater cafe, has spent up to $200 per test to weed out drug users at her Port Taranaki business.

"I've spent somewhere in the low thousands," she said. "I think it's an investment. I only want people working their best, whatever their best level is."

SIMON O'CONNOR/Fairfax NZ Barbara Olsen-Henderson, owner of Bach On Breakwater cafe, said countless Kiwis fail drug tests while overseas workers are never an issue.

Olsen-Henderson voiced her concerns about the normalisation of drug culture in the country, backing Prime Minister Bill English's recent comments about the hospitality industry's struggle to attract and retain drug-free Kiwis.

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Last week English caused a storm when he said several businesses a week complained to him about their problems getting Kiwi workers to pass a drugs test, which explained why they were bringing in staff from overseas.

"One of the hurdles these days is just passing a drug test," the prime minister had said in the wake of record immigration.

"Under workplace safety you can't have people on your premises under the influence of drugs and a lot of our younger people can't pass that test."

Olsen-Henderson said she agreed with his comments.

She said the past few weeks had been met with continuous disappointment as she attempted to fill two vacant positions in her restaurant.

Under current rules, beneficiaries are required to pass drug tests if asked when applying for work.

"Of the first three applicants - all beneficiaries - the first woman said she wouldn't pass the drug test," Olsen-Henderson said.

"I held the job for two weeks for her to get her act together and have a clear test, but she abandoned the position the day before the test."

Olsen-Henderson said the second applicant was confident of passing the test, but did not.

"I held the position for her and she is now 'clean' and happily employed."

And the third applicant said they would pass but did not turn up for the drug test.

"[She] finally emailed to thank me for the opportunity but to say that she only smoked 'socially' but probably wouldn't pass the test."

A fourth applicant was a French woman on a holiday work visa who passed the test with no issues and is currently employed, Olsen-Henderson said.

"I have to say here that WINZ [Work and Income New Zealand) have been very embarrassed by our drug test results of the people they're offering as job-seekers," she continued.

"I'm considering asking them to drug test first at somebody else's expense to save me $90 a pop."

Olsen-Henderson said she introduced a drug-free policy at her New Plymouth cafe in 2011 after the discovery of a former employee's serious addictions.

"He was very trembly and tense all day and then he'd be great and having good days," she said.

"Turns out he was on the methadone program and I didn't know that."

The worker also allegedly smoked marijuana and swallowed valium taken from his grandmother.

"He was nice but he would scare the staff, and he would scare me because he was unpredictable."

After Olsen-Henderson fired the employee and initiated the policy, she warned two other staff members they would be drug tested.

One disappeared and the other resigned, she said.

But Olsen-Henderson said a failed test did not necessarily mean a job loss.

She gives potential and current employees with "non-negative results" two options.

"They have a choice to stand down until they can have a clear test, so that they can give up," she said.

"Or if they're in real dire straits, I'll support them through rehabilitation if they want it."

Olsen-Henderson believes this approach could ultimately help drug users.

"Anybody can change and I know that, but they have to want to."

Although she forks out $90 to $200 per test, , she said it was an investment that gave her the reassurance her business was being run by people she could trust.

Although English was accused by critics of using anecdotal evidence ahead of the election season, on the back of record immigration figures showing 71,300 more migrants arriving in New Zealand than leaving in the year to January, Olsen-Henderson said she agreed with him.

"Mostly my problems are when I'm about to employ someone. It's that they don't pass a drug test," she said.

"It does really seriously narrow my pool of prospective employees.

"But, the non-New Zealanders always pass."

Olsen-Henderson said drugs were "one of the scourges of society" and she despised the idea that they were "becoming the norm".

While she couldn't say for sure why overseas workers had never failed a drug test for her, she hoped to help the Kiwis who did not pass.

"A lot of them are really good people. I think it's helpful for them," Olsen-Henderson said.

"But people don't have to work for me. Work for somebody else."