Sana'a: Yemen's opposition has drawn tens of thousands of people to the streets to rally against President Ali Abdullah Saleh's three-decade-old rule, but by noon the protesters quietly vanish.

Many head straight from the streets to the souk, or market, to buy bags stuffed with qat, the mild stimulant leaf that over half of Yemen's 23 million people chew daily, whiling away their afternoons in bliss, their cheeks bulging with wads of qat.

"After I chew I can't go out. When I chew qat, the whole world is mine. I feel like a king," said Mohammad Al Qadimi, a student who has attended Yemen rallies but said it would be hard to motivate himself to protest all day.

Yemenis are not known for being passive. Nationals disgruntled with their government have kidnapped foreigners and locals, ambushed security forces and occupied state buildings to extract concessions. But for many, qat time is sacrosant.

"When we have protests, they quiet down quickly because of this Yemeni habit. Qat is a negative influence. Every afternoon people go chew qat and the protests don't last more than a few hours in the morning," journalist Samir Gibran said, as he sat chewing qat with friends. He said he only chews once a week.

Qat, Yemen's top cash crop, ravages the economy and sucks dry dwindling water resources, economists say. Saleh launched a campaign against the bitter-tasting narcotic leaf a decade ago, but the population still spends millions of dollars a day on it.

"I'm going to the souk right now to buy qat. I'll have lunch, and then I'll chew qat with friends," said Ahmad Saleh, as he left an opposition protest. "In Yemen, people protest in the morning, but in the afternoon they go to chew qat."

"Qat time is from one to two in the afternoon. It's not possible for a protester to use that time for something else. For him, qat time is the most important," said Marwan Al Qalisi, an accountant in Sana'a, his cheek bulging with qat.

Qat, which sucks up around 40 per cent of Yemen's rapidly dwindling water resources, plays such a large role in the country's economy that the central bank calculates indicators both with and without qat. The plant accounts for 6 per cent of Yemen's GDP and a third of its agricultural GDP.

The World Bank estimates that Yemenis spend a tenth of their income on the plant and lose about 25 per cent of potential work hours to qat chewing.

Economists are torn about how to tackle Yemen's qat addiction, which can be a blessing as much as a curse.