Billionaire George Soros has thrown his weight behind California's marijuana legalization measure with a $1 million donation a week before the vote.
The contribution reported Tuesday by The Sacramento Bee is the single biggest donation from an individual other than Proposition 19's main sponsor, Oakland medical marijuana entrepreneur Richard Lee.
Mr. Soros, who has long campaigned for drug policy reform, said laws against cannabis were "clearly doing more harm than good" and had not stopped it becoming the most widely used illegal substance in the US and other countries.
Perhaps the most famous ever hedge fund manager, Soros said: "Regulating and taxing marijuana would simultaneously save taxpayers billions of dollars in enforcement and incarceration costs, while providing many billions of dollars in revenue annually."
Mr Soros said California had a chance to provide "national leadership" just as the repeal of alcohol prohibition in the US began with individual states.
He said that even if the measure did not pass, the fact that the vote was being held at all "elevated and legitimized public discourse" about the issue.
The beneficiaries of current US laws against the drug were criminal organizations in Mexico, he said, who would lose their competitive advantage if it was made legal.
"Like many parents and grandparents, I am worried about young people getting into trouble with marijuana and other drugs. The best solution, however, is honest and effective drug education," Mr Soros said. "I'd much rather invest in effective education than ineffective arrest and incarceration."