A third of cannabis users say they have driven while under the influence while more than 40 percent say they use the drug for medicinal purposes.

The 2012-2013 New Zealand Health Survey into cannabis use was released this week and found that 11 percent of the 13,000 adults interviewed for the study reported using cannabis.

Photo: AFP

Cannabis remains the most commonly used illicit drug both worldwide and in New Zealand, and the survey found that more than a third of cannabis users report using it at least weekly.

Maori and adults living in deprived areas are more likely to use cannabis.

Of the people surveyed, 36 percent said they drove while under the influence of cannabis, a trend that was more prevalent among men aged 35 to 44.

The executive director of the New Zealand Drug Foundation, Ross Bell, said until the police had the technology to test drivers for drug use, more officers need to be trained in basic impairment tests.

He said the tests were proving accurate, but not enough officers were trained to conduct them, and not enough of them were being done.

Medicinal use had higher reported rates among cannabis users aged over 55, and 42 percent of all users said they used the drug medicinally, the majority by smoking it.

Mr Bell said smoking anything wasn't the best way to ensure benefits from medicinal properties, so safer ways of delivering the drug were needed.

He said because medicinal users were buying cannabis off the black market, there was no way of guaranteeing its quality.

Eight percent of cannabis users reported a time in the last 12 months that cannabis use had a harmful effect on their mental health.

Younger cannabis users, aged 25 to 34, were most affected, with reported harm to mental health "decreasing markedly by age 55+ years", the study said.

Two percent of cannabis users reported experiencing legal problems because of their use in the last 12 months.

Women, people aged over 55 and those of Asian ethnicity had higher rates of reporting that they never use cannabis.

The Alcohol Drug Helpline can be reached on 0800 787 797.

Access the latest cannabis use data on the Ministry of Health's website