Britain's "hopelessly out-of-date" drug laws could now be debated in Parliament after 100,000 people signed a petition.
The success of Caroline Lucas' campaign has prompted Russell Brand to promise to "snog" the 100,000th signatory live on Channel 4 News.
Brand's endorsement, plus the intervention on Sunday of Nick Clegg, has helped drive support for the petition, which must now be considered for debate by Parliament's Backbench Business Committee.
It urges the Government to order a cost-benefit analysis and impact assessment of the Misuse of Drugs Act 1971 within the next 12 months.
Lucas argues that, as the Government is spending £3 billion a year on its drug policy, it is worth "checking whether Britain's current approach is value for money or money wasted".
The campaign saw a surge in support after Brand joined up with online campaign group Avaaz to encourage its 1.1 million members to sign up.
Brand said: "Almost 2,000 young people die in the UK each year from taking illegal drugs of uncertain potency, that they can only get hold of on the illegal market. Leading police, doctors, and politicians agree prohibition has completely failed to curb addiction and instead is costing the UK £3 billion a year."
Alice Jay, Avaaz campaign director, said: "This petition shows people want politicians to step up and change Britain's disastrous drug laws.
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"Experts agree it is one of the most counterproductive policies we have. The Government wastes £3 billion of taxpayers' money every year treating addiction as a crime rather than a disease. It's time to stop this madness."
The petition also surpassed 100,000 signatures shortly after Deputy Prime Minister Nick Clegg called for Britain to undertake a major review of drugs laws.
Writing in The Observer, Clegg said: "The UK can lead the debate in Europe and Europe can lead the debate in the world. But we must be prepared to start afresh with a new mindset and be prepared to do things differently."
Danny Kushlick, head of external affairs at Transform Drug Policy Foundation, said: "The level of public support for a debate on prohibition and alternatives demonstrates yet again that the public are way ahead of politicians on the issue of drug law reform.
"Polling indicates that over two-thirds of the UK public want a review of all policy options, including the legal regulation of some or all drugs."
Lucas added: "The Misuse of Drugs Act is hopelessly out of date.
"It has never been reviewed, or undergone a cost-benefit analysis.
"In England and Wales alone, an estimated £3 billion a year is spent fighting the war on drugs, to little effect.
"Over half of the people in prison are thought to have serious drug problems, and yet we continue to fail to treat drug addiction as the serious health problem it is.
"I'm absolutely delighted that so many people have sent a clear message to the Government that we need a fresh approach. Today we have achieved an enormous step towards an evidence-based drugs strategy."
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