The quest to find the magic diet pill knows no limits. Of course, the path is littered with failures in the form of embarassing side effects, heart and lung damage, suicides, lawsuits and, more recently, FDA rejection. Think fen-phen. Think Acomplia. Think Xenical and orange undies.

But the obsession with looking slimmer and the adverse consequences brought on by excess weight - high cholesterol, high blood pressure, diabetes - make obesity too compelling - translation: potentially profitable - to ignore. And so BusinessWeek takes a look at three of the more interesting prospects that are currently intriguing researchers, investors and, soon enough, regulators. Whether any will succeed, well, don’t give up your diet yet.

Take Vivus, a small company that is testing Qnexa, a mix of phentermine and topiramate. Phentermine was never implicated in the heart-valve issues that caused fen-phen to be recalled and remains on the market, but can make people very jumpy. Topiramate, an epilepsy treatment that J&J tried to rework for obesity, causes the mind to scramble at high doses. But Vivus believes they cancel each other out - phentermine is a stimulant and may wake up parts of the brain suppressed by topiramate. Some obesity specialists are skeptical. “If we use these drugs together, I’m concerned that we could create a cadre of thin zombies,” Robert Lustig, a professor of clinical pediatrics at the University of California at San Francisco, tells the mag.

Merck, meanwhile, is developing a drug that works like Sanofi’s Acomplia by affecting the brain’s cannabinoid receptors, and the resemblance is a bit close for comfort. “It’s not trivial,” says John Amatruda, Merck’s vice-president for clinical research. So Merck added an extra year on a two-year trial to gather more data. But a recent small 12-week study found about 30 percent of patients reported psychiatric side effects such as depression versus 18 percent on placebo. Merck says side effects were worse at high doses, so FDA approval will be sought for low doses. But whether these produce impressive weight loss is another matter.

Then, there’s Amylin, which is combining leptin with its own pramlintide, an unusual approach because this combines two hormones the body makes naturally. Given together, they seem to trick the body into resetting itself to a lower weight, the mag writes. In November, data showed patients lost nearly double what people typically lose on Xenical or Meridia. But large-scale human trials don’t begin until next year at the earlier. The 25-pound average weight loss in the trials “was astounding,” ceo Dan Bradbury tells BusinessWeek. But he’s quick to add, “we don’t know what it’s going to do long term.”