Saturday marks 90 years since using cannabis was banned in New Zealand.
The Dangerous Drugs Act was passed in 1927, and rallies to get rid of the law will be held in Auckland and Wellington.
Cannabis Armistice Rally organiser Chris Fowlie says countries that have legalised the drug don't have the same synthetic abuse problems that New Zealand has.
"When you ban things you push it underground and make it more dangerous," he told Newshub.
"You can see that not only with synthetics, but natural cannabis itself where you have medical users who are forced to go to gang-run tinny shops to get their cannabis."
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The death of a Hutt Valley man this week may be linked to synthetic drug use, with police making multiple seizes and arrests in the area.
"If we want to make it safer for people… you have to regulate it," said Mr Fowlie.
The Government will hold a referendum to legalise personal use of cannabis by the 2020 election.
"We have a new Government and a new way of thinking, and we are really looking forward to medical cannabis being legalised and for the country having a really good discussion over the next couple of years," said Mr Fowlie.
Synthetic drugs can be up to 50 times stronger than natural cannabis, experts say, with the average product on offer around 10 to 15 times stronger.
"Even a single smoke of synthetic is the equivalent of up to 15 normal joints. This is why the effect is so very different and so very dangerous," says Wellington Hospital emergency medicine specialist Dr Paul Quigley.