The president of the Aotearoa Legalise Cannabis Party has announced he's defecting to Gareth Morgan's The Opportunities Party (TOP).

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Abe Gray, who is also the founder and curator of the Whakamana Cannabis Museum in Dunedin, has sent a letter to all Cannabis Party members encouraging them to join him to help TOP reach the 5 percent threshold to enter parliament.

Mr Gray told Morning Report he supported the Cannabis Party because it was the only one willing to speak about the issue, but that had now changed.

"There's been a sea change in the public opinion attitude. But of all the parties who are posturing themselves now, the Opportunities Party is the only one that has a real, deliberate, well thought out policy, and one that's backed by evidence.

"And it has basically eclipsed the Cannabis Party and there is no reason why I wouldn't want to support TOP over them."

He said the Cannabis Party had attracted criticism in the past for being a single-issue party and for not having the profile or the resources to get its message across.

"I think you will see a mass exodus from the party over the coming weeks and months.

Mr Gray said he submitted his resignation to the Cannabis Party this morning.

Official figures show the party received just under 11,000 votes in the 2014 election.