Police introduced a formal pre-charge warning in 2010 aimed at reducing the number of low-level offences going through court. A pre-charge warning results in an offender being arrested and processed at a police station, but the warning does not appear on an individual's criminal record.
Mr Vigor-Brown thought the warning system worked well.
For young people, often a warning from the police is enough to reinforce the seriousness of their predicament.
"The mere fact of a warning for the greater percentage of people is just enough to say, 'I'm not going near that again'."
In a statement, police spokesman Tim Anderson said: "Our officers have discretion to warn for offences and police deal with these on a case by case basis.
"In terms of an arrest, every case is judged on its merits and sometimes an arrest is made to enable that individual to get some treatment for the drug problem they may have at the time."
Sensible Sentencing Trust Rotorua spokesman Peter Bentley said society should be wary. "It's seemingly decriminalising drug use and is devaluing the justice system. If there was something like a 90 per cent conviction rate they just wouldn't do it.
"If they get caught and there is absolutely no consequences they think they will get away with it. A verbal dressing-down does not have the same effect as a conviction," he said.
Te Utuhina Manaakitanga addiction service manager Donna Blair said the best thing for low-level offending was to provide education and counselling.
"We consider the possible consequences and work towards positive change and healthier lifestyles. While having a conviction stifles people's potential, it is not the end of the world if supported to address addiction issues and seek healthier lifestyles," she said.
Drug Foundation executive director Ross Bell said fewer convictions for low-level drug offences was the right direction.
Drug offences:
* 195 drug-related offences in 2015.
* 60 cases resulted in no court action.
* 36 cases resulted in informal warnings.