At 9:30 a.m. on Thursday, 12 boxes of alli, the first FDA-sanctioned diet drug to be sold without a prescription, were placed on the top shelf of a Santa Monica Walgreens' diet section. Four hours later, all but one had been sold.

"I have never in my life experienced anything like this," store manager Roe Love, a pharmacist for 20 years, said as she eyed the empty space next to the last box of 90 capsules selling for $59.99.

The fact that the product is kept with the rest of the diet drugs under locked glass on the shelf -- to prevent theft -- didn't deter people from requesting it.

The only comparable phenomenon Love could think of was the frenzy over the antibiotic Cipro during the post-9/11 anthrax scare. "You couldn't fill those prescriptions fast enough," she said.

The latest diet pill is being rolled out across the country this week by manufacturer GlaxoSmithKline. The company's website, myalli.com, and literature offer the potential for greater weight loss than dieting alone if you do everything right and a warning of extraordinarily unpleasant and embarrassing side effects if you don't.

Not all merchants have alli (pronounced "ally") in stock yet -- a spokeswoman for Longs Drugs says all stores should have it by Saturday -- but among those that do, the buyers have overwhelmingly been women.

"And they're not fat," Love said of the women she saw buying the drug at her store.

In Los Angeles, where thinness is the Holy Grail and people will do just about anything to get there -- including risking some rather unfortunate intestinal distress -- buyers didn't flinch at possible side effects.

The drug was introduced as the stronger, prescription-only Xenical several years ago.

It works in the digestive system by blocking the absorption of about 25% of fat that is consumed.

In a theoretical 3,000 calorie-a-day diet with about 100 grams of fat, the drug would eliminate about 225 calories.

But it can also result in what the manufacturer describes as loose stools and gas with an oily discharge. "It's probably a smart idea to wear dark pants, and bring a change of clothes with you to work," the drug's official website says. (The drug maker's literature and website say side effects can be minimized with a low-fat, reduced-calorie diet.)

But the women buying alli Thursday were unfazed by the warnings.

At a San Fernando Valley Walgreens that had sold 10 boxes -- with one man among the buyers -- no one was asking the pharmacist about side effects. " 'Will it work?' That's the only question they're asking," said the store's pharmacy manager, who spoke on condition of anonymity.

At a prominent display in a Rite Aid drugstore in Santa Monica, prospective buyers clutched the big alli starter kit and shared war stories from the diet battleground.

"I've tried so many other things," said Monique Brown, a Santa Monica legal secretary who says she's been through Metabolife, CortiSlim and various products, some of which made her jittery. She dreams of losing 30 pounds.

At least, alli won't make her jittery, she said. "I'm just willing to give it a try. There are side effects to a lot of things.... I work in an office and I sit all day. There's a bathroom right there. We've all worked together a long time. If you have to go, you have to go."

Wendy Reid, a 57-year-old Tallahassee, Fla., resident visiting Southern California, said she had no qualms about taking alli. "I've read about it completely," said Reid, carrying her purchase out of the Rite Aid in Santa Monica.

Deeply tan from her daily regimen of tennis, she nonetheless has 15 extra pounds she says she gained since she hit menopause. She shrugged off the possibility of side effects. "I thought I would just deal with them," Reid said. "So far it's been proven safe."