The Global Drug Survey has found one in eight people had been asked by their employer to take a drug test.

But it also showed workplaces could be right to worry. More than a third of full-time workers surveyed said they had taken drugs or alcohol within two hours of starting work, and some had even begun to use newly invented psychoactive drugs in a bid to stay one step ahead of the testers.

Ken Pidd, the deputy director, research, at the National Centre for Education and Training on Addiction, said the tests were a growing trend. ''Obviously the biggest threat from workplace drug use is safety, if people are intoxicated at work. But there is a much larger picture around absenteeism, or even presenteeism, related to use outside the workplace,'' he said.

He recently conducted a review of the evidence in favour of the tests, and found that outside a few circumstances - such as mandatory alcohol testing for US truck drivers - there was little proof they improved safety. ''It is a particular issue for urine testing, which doesn't actually detect impairment, just prior use,'' he said.

Dr Pidd said studies had found the overall drug and alcohol use in the workplace in Australia was relatively low, although in some industries, such as hospitality and finance, rates were far higher.

''Workplace drug use tends to be in line with drug use in the broader population,'' he said.

He said prescription drugs posed a particular problem for people returning to work from injury, as they could exacerbate problems by doing more damage with dulled pain sensations.

Dr Pidd expected workplace drug testing to increase, but said less expensive methods such as information or counselling sessions could sometimes be more effective.