Eight people suffering from severe reactions to synthetic cannabis have been treated at Christchurch Hospital's emergency department with three admitted to intensive care.

Photo: 123RF

Emergency medicine specialist Paul Gee said the patients had come in over the past 24 hours.

All of the patients are men, aged 20 to 56 years.

Dr Gee said there had been a noticeable increase in the number of people showing up at the emergency department suffering side effects from synthetic cannabis including a man last month who went into cardiac arrest.

Toxicology results show patients had taken either AB or AMB-FUBINACA which have been linked to numerous deaths in the North Island over the past year.

The Canterbury District Health Board is warning synthetic cannabis users in Canterbury that they should be extremely cautious.