The Cannabis Party's plans to offer exclusive tours to California to buy legal cannabis have been thwarted by Ministry of Health advice.

The ministry and Customs today released new information to travellers entering New Zealand from the United States with medical cannabis products.

"Cannabis-based products supplied in the United States of America cannot be carried with you when entering or leaving New Zealand," the ministry said.

Although some US states allow medical use of cannabis, the products do not have US Food and Drug Administration approval, the ministry said, so are not considered "lawfully supplied".

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Before the ministry's update, the Cannabis Party claimed on its website a loophole in the misuse of Drugs Act meant medical cannabis could be brought into New Zealand if it was legally obtained abroad.

The party last week announced its exclusive guided tours of California to buy legal cannabis.

Mt Roskill byelection candidate Brandon Stronge said the tour "was a unique opportunity for medical cannabis users to bring cannabis back into New Zealand legally".

A doctor's evaluation and medical cannabis recommendation were advertised as part of the package, costing about $5000.

Ministry of Health spokeswoman Charlotte Gendall said the updated rules had not been put in place in light of the Cannabis Party's California Tour plans.

"It's part of ongoing progress about keeping the public well informed. It's not as a result of any outside influence."

Gendall added that if the Cannabis Party attributed the new update in rules as a response to their California plans, that would be "untrue".

Cannabis Party leader Julian Crawford said the ministry's updated rules were "interesting timing".

"It's very unfortunate for the people who have medical conditions that are suffering, and actually need cannabis."

Crawford said much of the confusion had come from what Customs had previously said.

"They've been allowing people into the country up until recently with products from California so I don't know what's changed. The law hasn't changed, it's just their interpretation of it."

The party leader said they were "still keen" to ahead with the California tours.

"People can enjoy visiting the dispensaries in California, but we probably won't be able to bring it back into the country until this is clarified further. Hopefully this position will be clarified in court at some stage as well."

Crawford added that he would be following developments.

"Until then we'll just wait and see what happens."