A leading drug researcher believes the rise of methamphetamine has been a major factor in declining arrest rates for cannabis possession over the last two decades.
New Zealand has seen the number of arrests for cannabis possession half since 1991, even though it remains a criminal offence under 30-year-old drug laws.
Massey University researcher Chris Wilkins believes the emergence of methamphetamine, or "P", in the early 2000s brought about a dramatic shift in how the criminal justice system responds to cannabis offences.
He told TV ONE's Breakfast that police were forced to take action when "P" came to prominence 10 years ago.
"I think we have to put this in the context of the rise in meth
and their (police) need to respond clearly to that. There's always
a new set of priorities," said Wilkins.
Wilkins also believes a generational change has affected declining arrest rates as police become more pragmatic in how they deal with the Class C drug.
"I think it's a generational change in terms of police on the beat. They have the opportunity to give to warnings and be more pragmatic in how they deal with cannabis use."
He said judges have also become more lenient in the sentences they hand out to criminals convicted of marijuana possession.
"It's not so much a clear change in terms of the law but more people involved in the criminal justice system responding differently."
New Zealand's rate of arrest follows international trends towards decriminalising cannabis.
In some states of Australia, cannabis users found with a small amount of the drug may face a fine or a notice to attend a mandatory counselling session.
However, Wilkins said some countries, such as the US and Switzerland, are taking a hard-line approach to the drug which has resulted in an increasing number of arrests.