George Soros gives $1m to California's pro-cannabis campaign

California's campaign to legalise marijuana received a major boost today with a $1m donation from billionaire financier and philanthropist George Soros.

The cash infusion, one week before Californians vote on a measure that would let anyone over 21 grow and possess up to an ounce of marijuana and allow local councils to tax sales of the drug, marks the first major investment by Soros in the mid-term elections.

Soros, a prominent donor to Democratic organisations in 2004, 2006 and 2008, told the New York Times that he was sitting out these elections because the prospects were so bleak.

"I don't believe in standing in the way of an avalanche," he told the Times. Soros has focused instead on funding research into climate change policy, committing to spending $10m a year over the next decade.

But in an article posted in the Wall Street Journal, he argued that, no matter what the outcome on 2 November, California's legalisation campaign was a winner.

"The mere fact of its being on the ballot has elevated and legitimised public discourse about marijuana and marijuana policy in ways I could not have imagined a year ago," he wrote.

Soros is a longtime proponent of legalisation. He spent $3m on initiatives that led to the legalisation of marijuana for medical use in the 1990s.

Recent opinion polls suggest, however, that Californians are unlikely to opt for full legalisation – although some commentators have speculated that people may just be reluctant to come out in favour of marijuana in public.

The Soros donation could alter that dynamic. The donation became public 48 hours after the no side began television and radio ads warning that legalisation would be an utter disaster, with truck drivers and hospital personnel doing drugs on the job. "Imagine coming out of surgery and the nurse caring for you was high," said one ad.

For its part, the legalisation campaign is running ads featuring former police chiefs claiming that bringing marijuana into the open will prevent the rise of Mexico-type cartels and generate revenue for cash-strapped town councils.

The Soros donation is the largest from a single individual since Proposition 19's sponsor, Richard Lee, put down $1.5m of his own money in support of legalisation.

Lee, a former lighting technician for Aerosmith, has made a fortune from indoor grow houses and dispensaries for marijuana in Oakland.