NEW YORK (CNNMoney.com) - A California biotech could be on its way to a diet drug blockbuster or tiptoeing through a minefield depending on the performance of its next miracle weight loss treatment.

Amylin (up $1.65 to $44.41, Charts), the San Diego company that's seen its stock price triple over the last 12 months, is trying to break into the lucrative but risky $40 billion obesity market with an experimental drug combination. Tests on the pramlintide-leptin combo are still in their early stages, with human trials yet to begin. But the biotech, best known for its diabetes drug Byetta, has good reason to get excited: corpulent rats lost 12 percent of their body weight in pramlintide-leptin tests. If those results are repeated in humans, then a 300-pound man could lose 36 pounds just by taking drugs.

"Now that we know the combination of the two works in obese rats, we're going to see if it works in obese men," said Amylin's senior vice president of research, Dr. Alain Baron.

Baron said that pramlintide, when taken alone by humans, triggered more than 3 percent weight loss in experiments, while leptin alone did nothing at all. He said that human tests with the combo will begin this year "to see if it's worthwhile going forward."

Amylin faces two enormous challenges along the way. The first challenge is obvious: the drug could achieve radically different results in humans than it did in rats. The second challenge is often ignored by that one-third of the American population that's overweight and desperate to lose: the obesity industry is littered with side effects and other risks.

Remember fen-phen? That's the diet drug combo that Wyeth (up $0.09 to $43.69, Charts), formerly known as American Home Products, pulled off the market in 1997 after it was linked to heart valve disease. Two years later, the company paid a $3.75 billion settlement to thousands of former fen-phen users.

The safety profile for pramlintide-leptin has been good so far, sad Baron. "It's been extremely safe," he said. "We've not seen any toxicities."

If Amylin's combo ends up being free of noticeable side effects, that would certainly give it an edge over its competitors. Roche's diet drug Xenical causes diarrhea (a recurring theme in weight loss medications) while Meridia from Abbott Labs (up $0.21 to $42.43, Charts) can ramp up blood pressure and heart rate.

Both those drugs are on the market and well-known to patients and physicians. But getting analyst sales projections or an estimated FDA filing date on Amylin's pramlintide-leptin combo isn't easy, because experiments are still in the embryonic stages.

"It's still too early to tell and I haven't even included this combination in my estimates," said Biren Amin, analyst for Stanford Financial Group. "At this point, even if the drug works - and we're not certain it will - it will probably not be launched until the next decade."

But Amin said there's one thing investors can be sure of: competition.

Other drugmakers recognizing the money-making potential in weight loss drugs and are hard at work to develop new ones. The most immediate candidate is Sanofi-Aventis' (up $0.74 to $46.35, Charts) Acomplia, which is a diabetes treatment, not a diet drug, though weight loss is one of its many indications. Acomplia was approved by European regulators today and is currently being reviewed by the Food and Drug Administration. In addition, GlaxoSmithKline (up $0.53 to $55.02, Charts) is trying to introduce an over-the-counter version of Roche's Xenical into the market.

Amin does not own shares of Amylin stock and Stanford Financial does not do business with them.

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