Oliver Stone's latest movie pits a pair of Californian neo-hippy cannabis growers against Mexican drug barons aiming to move their business north of the border, with predictably violent results.

In what he stresses is fiction, Stone's Savages returns to the theme of drugs and violence that helped make his name in Midnight Express (1978) and Scarface (1983).

The film, based on the critically-acclaimed book Savages by US author Don Winslow, tells the story of two Californians -- Ben (Aaron Johnson) and Chon (Taylor Kitsch) -- and their joint girlfriend Ophelia (Blake Lively).

They divide their life between surfing, smoking, shopping and a flourishing cannabis-growing business.

Everything is going swimmingly until a cartel run by Elena (Salma Hayek) suggests an alliance. Ben and Chon refuse, prompting heavies played by Benicio Del Toro and Demian Bichir to kidnap Ophelia.

The two hippies decide to take up arms and launch a merciless fight against the cartel.

"This is a hypothetical fiction. This is not Traffic, said Stone, referring to Steven Soderbergh's 2000 movie. "Traffic was a wonderful movie but it's much more documentary-like.

"But this one is hypothetical. It hasn't happened yet," he told reporters at a recent film promotion in Beverly Hills.

As usual, Stone has done considerable research and met a lot of people in preparation for making the movie, and he says he learned a great deal about drugs and violence.

"There has not been any kind of major violence on this side of the border yet," he said, compared to the 50,000 deaths since the launch of Mexico's military crackdown on powerful cartels in 2006.

"It's in the interest of the Mexican cartels to keep it south because if they start to move here, they're gonna get a lot of bad publicity and there's gonna be a lot of consequences."

But he acknowledges that cartels are not completely absent in California.

"They are here, they are growing. We know that. There's been busts. They may have deals here in California because the best laboratory in the world in now here," said Stone.

The director, a staunch supporter of decriminalising drugs, trumpets the quality of Californian cannabis, the sale of which is legal in the Golden State for medical purposes.

"We do have an independent growers market here, which is like a boutique business, and they are very good people. They grow great stuff, the best I've ever had in 40 years," he said.

If Stone's sympathies clearly lean towards the neo-hippies, his director's eye does not shrink from showing the grisly violence and wrenching choices that are part and parcel of the modern drug trade.

"We show some of the cruelty. We didn't show all of it because it's too rough. But you certainly have to deal with it. If you do otherwise, you're just sanitising the situation," he said.

He chose Mexican actress Hayek to play the cartel's merciless female chief.

"She's tough. She came from Mexico, she just propelled herself to Hollywood. I guess she didn't speak much English when she got here," he said.

"I met her years ago, when I did U Turn, and the first time I met her, she said: 'You son of a bitch, you didn't even see me for U Turn. You gave it to Jennifer Lopez.' I was stunned," said Stone.

For his latest film "I wrote her a note in Europe and I just said: 'You're the one.' When Universal asked me: 'Is she tough enough?' I said: 'Oh yes, she's tough.'"