LOS ANGELES (Reuters) - Comedian Cheech Marin, one-half of the most famous pot-smoking duo of the 1970s, lent his celebrity to a medical marijuana convention that opens on Friday in Los Angeles, and used the occasion to plug a new movie.

The documentary of Marin’s reunion last year with his longtime partner, Tommy Chong, for their first tour in over 25 years, is set for release by the Weinstein Co. in theaters, on DVD and video-on-demand on April 20, a studio spokesman said.

The release date, 4/20, corresponds not so coincidentally to the numerical code widely recognized within the cannabis subculture as a symbol for all things marijuana.

Posters for the “Light Up America” movie bear the tagline: “Their first joint venture in 25 years.”

Marin, 63, appeared at the L.A. Convention Center on Thursday for a news conference promoting HempCon 2010, a three-day conference touted by organizers as the first such gathering devoted to the medical marijuana industry.

Organizers said at least 40,000 tickets to the event have been sold, about double the advance sales for the 30th anniversary “Star Wars” convention in Los Angeles in 2007.

Marin said he supports “across-the-board” legalization of pot with restrictions similar to those for alcohol.

“It’s a movement whose time has come. It’s inevitable,” he said. “Society since the Bible has needed a socially acceptable intoxicant, and here it is. This has been our drug of choice. It’s ... much healthier, has more benefits than alcohol.”

Chong, 71, did not make it to the news conference, though he had been expected to attend. Marin said he was absent due to a death in the family.

The two performers became one of the most successful comedy teams of the 1970s with an act based on their brand of pot-influenced humor. After their reunion, they returned to the road this year for a follow-up tour dubbed “Get It Legal” -- an homage to the movement for liberalization of marijuana laws.

Cannabis advocates recently collected more than enough signatures to qualify for November’s ballot with a proposal to make California the first U.S. state to legalize possession and cultivation of pot for recreational use.

California led the nation in 1996 by approving the use of cannabis for medical purposes and enacted a law in 2003 allowing the drug to be cultivated and distributed to prescription-holding patients through nonprofit collectives.

But a public uproar was sparked in Los Angeles over the proliferation of hundreds of medical marijuana dispensaries after the Obama administration halted federal raids on the clinics last year.

Last month, the City Council voted to shut down most of the facilities. Medical marijuana proponents have vowed to challenge the ordinance in court and to seek to overturn it with a local ballot measure later this year.