The rising use of synthetic cannabis is having a significant impact on violence levels in mental health wards and a new law banning the substances is having no visible effect, a mental health director says.

Assaults on staff in Southern District Health Board Otago mental health services in the first seven months of the year were up about 37 per cent compared with last year, figures show.

Overall, assaults on staff in the board's health services in the province were up about 36 per cent on last year.

Otago mental health nursing director Heather Casey said that in some mental health services, synthetic cannabis was more prevalent than alcohol or illicit drugs.


Those using the synthetic substances were likely to be emotionally unstable, and lack inhibition.

"It's a huge problem," she said. "It is having a significant impact on wards."

A move to reduce the harm associated with synthetic cannabis, through temporary bans on 28 substances pending legislation to deal with the legal-highs industry, had made no visible difference.

Synthetic cannabis was available if people wanted it, whether on the internet or in the community, Mrs Casey said.

"All we can do is advise people not to use it - it is having a definite impact on mental health [wards].

"If people want it they are quite innovative at accessing it," she said.

Some inpatients on day leave were obtaining synthetic cannabis, then returning to the wards.

Legal highs were used by teens, but also by those in their 20s and 30s, she said. In the emergency psychiatric service, alcohol remained the biggest factor in assaults.

Mrs Casey believed also that the rise in assaults was the result of increased awareness and reporting. Staff were encouraged to identify what they considered an assault - including verbal attack - rather than using health board definitions.

National Poisons Centre toxicologist Dr Leo Schep said world-first legislation set to become law next year would hopefully solve the problem, through putting the onus of safety on to the legal-highs industry.