Mr Blair said he had worked for 17 years at the Dunedin youth agency, which had a Southern District Health Board contract to help 24 young people in Otago with moderate to severe alcohol, drug and mental health issues.
Many of the young people were smoking up to $60 worth of synthetic cannabis a day and were ''wheeling, dealing and stealing'' to sustain their habit.
''It's a vastly different world to what we were dealing with a few years ago.''
Several synthetic cannabis users told counsellors how smoking K2 made them vomit. Many referred to it as ''K-spew'' but continued smoking it, because they were addicted.
''It's a dirty drug and a lot of them don't enjoy it but they can't stop.''
Some synthetic cannabis users were ''zombie-like'', Mr Blair said.
''There is muscle rigidity and twitchiness and slurred and troubled speech.''
Counsellors had seen some ''hideous'' symptoms when young people were detoxifying from synthetic cannabis.
The ''shrewd'' synthetic cannabis manufacturers would find ways around the new legislation proposed in the Psychoactive Substances Bill, which would mean manufacturers had to prove its products had no more than a low risk of harm.
''They'll be working on it now ... these kids are just lab rats.''
Synthetic cannabis use had made the psychiatric ward at Wakari Hospital ''very busy'' and had caused the Early Intervention in Psychosis service to be ''flat out'' with University of Otago and Otago Polytechnic students suffering mental health issues from smoking the substance, he said.
Mental Health Directorate medical director Dr James Knight said about one in eight admissions in the mental health inpatient units earlier this year were associated with synthetic cannabis use.
Presbyterian Support Otago Family Works social worker supervisor Debbie Gelling said synthetic cannabis was having a ''huge impact'' on the support agency.
And more Dunedin families were seeking budgeting advice when family members were stealing to feed the habit.
''If someone in their family has been using K2 it can be an expensive habit.''
The Dunedin Collaboration Against Family Violence Te Rito co-ordinator Bonnie Scarth said synthetic cannabis was changing the dynamic of some Dunedin families.
''Mental health services and other agencies are getting lot of requests from families who struggle with it and have seen the behaviour changes of a loved one.''
