The amount of houses testing positive for methamphetamine contamination was also indicative of the growing methamphetamine trade, he said.
The trend was similar to the late nineties and early 2000s.
Mr Hardy believed the social impact would be a resurgence of "horrific unspeakable" crimes.
TDDA figures show cannabis was detected in 81.6 per cent of positive tests, up on 76.5 per cent the previous year.
Figures showed 11.8 per cent of positive tests detected opiates, compared to 12.2 per cent in 2014.
The proportion of positive tests showing synthetic cannabis use dropped from 3.8 per cent to 0.8 per cent.
Mr Hardy said there had been a decrease in the overall percentage of positive drug tests in forestry -- reflecting a behavioral shift to an intolerance for drugs in such industries.
He said the industry was very vigilant with testing and education programmes.
As well as preventing accidents in the workplace, the industry was addressing issues before they became a wider problem in society.
Mr Hardy said the rate of positive drug tests was also down in the transport industry.
He said it was normal practice for transport operators to have stringent drug and alcohol testing and to have TDDA regularly present to members about the dangers of drugs in the workplace.
However, the proportion of people testing positive for methamphetamine was up in both the forestry and transport industries.
Mr Hardy said that was a reflection of a national trend of methamphetamine becoming a much larger issue in New Zealand in general.
Hayden Loader, the general manager of civil engineering company Loaders in Whanganui, said the company had a mandatory pre-employment drug test as well as random and post-incident testing.
The company's clients could also require their own testing.
Mr Loader said tests kept workers clean and showed the company was serious about drug issues.
Workers who tested positive for drugs would leave work until they could provide a clean test then be given a final chance, he said.
Loaders' staff worked with heavy machinery and staff needed to know the person operating the machine wasn't under the influence.
"We just can't afford to take the risk," said Mr Loader.
He said the stigma around reporting colleagues who might be under the influence was slowly going away and the company always acted on workers' concerns.
Mr Loader thought drug testing was becoming more common in workplaces with mandatory drug tests becoming the norm.
Ravensdown fertiliser co-operative spokesman Gareth Richards said everyone was subject to a drug test before starting employment at the company.
The names of all staff were also put into a pool and could be randomly selected to be tested, he said.
Ravensdown offered free counselling to any employees stood down after failing to pass a drug test.
Ballance agri-nutrients general manager people and capability Edith Sykes said the company had a drug and alcohol policy to ensure that Ballance was a safe workplace.
"From our people making fertiliser and animal feed, to our sales team out on the road, to our office-based teams -- we want to send everyone home safely each day.
