Duncan Garner has done a U-turn on recreational cannabis.
He said he's had a "big rethink" about next year's vote, and believes the country is "on the brink of making a very serious mistake by softening the law".
"Seriously, why would our lawmakers send a message that effectively says, 'Cannabis: okay, but cigarettes: very bad'. We're trying to go smoke-free by 2025, so why are we doing this?"
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The host of The AM Show has in the past showed support for legalising recreational cannabis. He was impressed by cannabis advocate Rebecca Reider when she appeared on the show in November.
Asked by Garner why recreational cannabis should be legalised, Ms Reider flipped his question to ask why it shouldn't. Her response impressed Garner so much, he said it should go viral on social media.
"Prohibition doesn't work, people already have cannabis, the problem is that the quality's not controlled, it can be contaminated, it's sold on the black market by criminals, and people are going to prison over it," she said.
But Garner said on Monday he's all too familiar with the effects of "evil" drugs. He admitted that he's struggled with alcohol in the past, saying he's "scared to drink too much these days because I can't control myself".
"What's the best-case scenario here with weed? That more of our kids try it earlier because they hear this message that it's okay?"
Garner said he personally knows someone who's addicted to marijuana. The man is "meandering, he's muddled, he's a mess", Garner said, adding that he first tried the drug at school.
"Recreational weed - it's a mind-altering drug. Why would we put that into the hands of our young people who, more often than not these days, identify mental health as their biggest concern?" he said.
"Surely, cannabis isn't the answer to that. Sport, exercise, fresh air, a job, talking - that's the answer."
The Green Party was promised a referendum on legalising recreational cannabis at or by the 2020 election as part of their coalition agreement with Labour.