Two teenagers received hospital treatment after using a synthetic high drug on the same day the drugs were made illegal.
Psychoactive substances were banned from 12.01 today after the government passed emergency legislation banning them until they had been tested to be safe.
The teenagers in Upper Hutt were using "Illusion'', a synthetic high.
A Wellington Free Ambulance spokesperson said five teenagers aged 13 and 14 were smoking the drug when two became ill.
"Two were taken to Hutt Hospital in a moderate condition suffering from dizziness. One of them had collapsed at the scene,'' he said.
Police and Health Enforcement Officers have been visiting all 148 licensed retailers to ensure they weren't selling the products.
Inspector Rob Duindam of Police National Headquarters said police had been preparing for the operation today.
"Some hard work by Police and Ministry of Health leading up to today has ensured today's focus on enforcement and prevention ran smoothly.
Our staff report that retailers have been very positive throughout this process.''
"There will be ongoing visits to retailers to ensure psychoactive products remain off the shelves. This may include conducting controlled purchase operations to ensure sales are no longer occurring.''
Meanwhile, Christchurch police are continuing to hunt for a third person in relation to a theft of synthetic highs from a store minutes before the law came into effect.
Police said two men carrying knives held up and stole from a R18 store on Stanmore Rd in Linwood around 11.20pm.
A 30-year-old man and an 18-year-old man, both from Christchurch, appeared at the local district court this morning on charges of aggravated robbery.
The men were accused of punching the store owner and stealing a quantity of cash and synthetic drugs. The shop owner's injuries were not serious.
They were caught and arrested when police stopped a vehicle close to the store.
A third offender is still being sought by police.