Hundreds of patients are searching for a new source of medicine after NZ Post reported their dealer to police.

Medicinal cannabis patients are running low on supplies after a prominent dealer was arrested for sending drugs through the post.

His arrest has left terminally ill Kiwis scrambling to find new sources for the plant product they say helps relieve their pain and make life bearable.

"We're trying to find medicine so that we can survive," said Joan Cowie, a 64-year-old Aucklander who has stage four lung cancer.

MARTIN DE RUYTER/STUFF NZ Post said it had "a zero tolerance policy for illegal items being sent through our network".

"We're frantic, really."

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The 55-year-old West Coast grower was arrested in October after posties noticed the smell of cannabis coming from parcels and reported him to police.

CHRIS SKELTON/STUFF Joan Cowie has stage four lung cancer, and says she's "frantic" trying to find a new source of medicinal cannabis.

He has since appeared at the Greymouth District Court on a range of charges, including cultivating cannabis, selling/supplying cannabis oil, producing/manufacturing/distributing cannabis, procuring/possessing cannabis plants, and possession of cannabis oil for supply.

Pearl Schomburg, founder of Auckland Patients Group, which supports those using medicinal cannabis, said the man's arrest had left hundreds of users in the lurch.

Schomburg said he was one of the only cannabis growers in New Zealand who specialised in plants that were low in THC (tetrahydrocannabinol) and high in CBD (cannabidiol).

DAVID WHITE/STUFF Pearl Schomburg says the arrest of the West Coast grower has left hundreds of medicinal users in the lurch.

THC is the compound within cannabis that makes people high, whereas CBD does not produce any psychoactive effects.

"There are very few people that are interested in growing this strain, because it's low THC," said Schomburg.

"This is a man who took a risk planting and growing these plants when no-one else was interested."

CRAIG HOYLE/STUFF Pearl Schomburg uses medicinal cannabis to combat chronic pain she suffers due to RSI and rheumatoid arthritis.

Schomburg said low-THC cannabis products were particularly helpful for medicinal users, as it meant they could remain "functioning during the daytime" without getting high.

The 64-year-old great-grandmother, who suffers from chronic pain due to RSI and rheumatoid arthritis, added she had found the man's arrest particularly stressful as one of the packages intercepted by NZ Post had been addressed to her.

"My stress levels have gone through the roof, and I wake up most nights and vomit," she said.

CHRIS SKELTON/STUFF The new Labour-NZF-Greens government has promised a referendum on cannabis use by 2020.

"Police say they won't target patients, but I'm sitting here trying not to worry about that knock on the door."

Both Schomburg and Cowie keep paperwork to hand proving they are sick, in case they are ever challenged for being illegal drug users.

Shane Le Brun, coordinator of the charity Medical Cannabis Awareness NZ, said arresting medicinal suppliers was counterproductive.

ALDEN WILLIAMS/STUFF Shane Le Brun says patients will continue to illegally use medicinal cannabis, and the law needs to change.

"These people will be seen as martyrs and heroes to the patient community, and unfortunately it reflects poorly on the police," he said.

"Patients will continue to break the law, often with the support of their specialists, making criminals of otherwise law-abiding citizens."

NZ Post's Mark Baker said the service worked closely with police and had "a zero tolerance policy for illegal items being sent through our network".

"If a staff member believes that a mail item contains an illegal or dangerous substance we encourage them to notify their manager, who will often seek guidance from our security team."

Baker declined to answer questions about the West Coast arrest, saying NZ Post "would not comment on police matters".

The medicinal cannabis community is planning a rally in Auckland on Saturday, 11 November, to show support for growers and users who have been targeted by police.

The new government has promised a referendum on cannabis use by 2020.