"It's actually really sad, it's like going to your kitchen pantry and sucking on rat poison."
Synthetic cannabis is a form of drug where chemicals are applied to a plant base.
Macfarlane said he wanted to start an open wananga for people who were using or producing what he called "designer drugs".
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"We need to start a conversation with the people who are smoking it," he said.
"I don't know what we can do to end it, maybe the best people to answer that is those who are using it.
"We have to go right back to the start of this, to look at why they are smoking it, because in there we'll find our answers."
Macfarlane said synthetic cannabis often contained chemicals similar to fly spray, anti-freeze and rat poison.
"How can we regulate that?
"All the stuff they're putting in [it] is not meant for human consumption."
He saw the effects when a man he was mentoring died as the result of synthetic cannabis.
"It was on the eve of his 27th birthday, and he was a good guy, a real warrior battling drug addiction," he said.
"When we were burying him I thought to myself, 'something needs to be done about this'. Then the next week people in Auckland started dying."
Macfarlane said people weren't great at talking about using synthetic cannabis.
"With most people you don't realise they're doing it until the ambulance turns up," he said.
"We need to be engaging people in something better, that's the underlying problem."
He is now hoping to start the conversation and was open to sitting down with anybody who uses the drugs.
"There'll be no police, no social workers, just me; someone who understands that kind of life," he said.
"I want to ask them why they have to smoke that s***, it's a really important discussion we need to have.
"It's stuff we don't want happening, we don't need it here in Rotorua."
