The National Poisons Centre received 242 calls between October 2010 and March this year in which those calling named specific brands linked to their side effects.
The centre received 66 calls about K2 and 51 about Kronic until January. Such products as Kryptonite, Thai High, Everest and Illusion also featured frequently in the calls received.
The figures appeared to show banned products were being stockpiled. Kronic — banned in August 2011 — and K2 — banned in May last year — were both still being cited by users in January this year.
An insider last night warned that stockpiles of the legal highs were being dumped on the market at cut-rate prices. He said synthetic cannabis was being offered to retailers at up to a quarter of the price before they were banned.
Toxicologist Leo Schep said the centre had received 400 calls in which the product was not named. "We've seen an increase in the number of calls and that is of concern. It suggests there is an issue out there and some of those people are suffering serious side effects," he said.
He said the increase in calls could also have followed Government demands for manufacturers to print the helpline number on legal high packets.
Schep said there were concerns about withdrawal with the drugs coming off the market. "We don't know how to treat them ... there is nothing that works at this stage."
The Poisons Centre document has reports of serious side effects, with 47 vomiting and 41 suffering heart palpitations. Most people also reported hallucinations, drowsiness, seizures, shaking and anxiety.
Legal high lobbyist Grant Hall, general manager of Start Trust, said the figures "proved these products are low-risk". He said they reflected a fraction of the 10,000 people who smoked legal highs daily.
"We get that data and products can be tweaked and if they pose more than a low risk of harm the authority can remove them, like they have been doing," he said. "There has never been a fatality in the last few years."
Hill said stockpiling was a concern because it created a black market where the products were unregulated.