Linda Forbes, who had organised regular protests outside Oamaru dairies since December, said the protesters had been unfazed by the dampening, and would hold another protest tomorrow.
Earlier this week Associate Health Minister Peter Dunne announced two substances included in the synthetic cannabis K2 product would be banned from May 9, but Mrs Forbes said she had little confidence anything would change.
"All they will do is say they have removed the ingredients and carry on selling it."
Tom and Cheryl Johnston said they had protested yesterday because Mr Johnston's son was hospitalised after he had an accident while high on synthetic cannabis.
"He decided to have a session on K2 and then decided to puff petrol.
"He had just got a job and been offered an apprenticeship and now it looks like he may lose it, all because he decided to come and buy this stuff," Ms Johnston said.
Mr Johnston said his son suffered first, second and third degree burns to 17 per cent of his body, and may need skin grafts once he was out of hospital in another two weeks.
The owner of the dairy declined to comment.