The story of Gilead Sciences' (NASDAQ:GILD) blood-pressure drug candidate, darusentan, went downhill rather fast.

It hit a peak in April when initial results suggested that the drug worked. It passed its first phase 3 trial leading to a nice little pump in the share price.

When the full data were presented at a scientific meeting a month later, things started to unravel. Heart-related side effects were revealed and the stock took a hit. But the side effects weren't necessarily bad enough to keep darusentan off the market, because the drug was being tested in patients who aren't able to get their blood pressure under control with other medications like AstraZeneca's (NYSE:AZN) Zestril, Merck's (NYSE:MRK) Cozaar, or Pfizer's (NYSE:PFE) Norvasc. Besides, a second phase 3 trial would clear up just how bad the side effect profile was.

Well, maybe not. In results from the second phase 3 trial revealed Monday night, side effects weren't even mentioned because the drug didn't pass its efficacy endpoint.

The company could roll the FDA dice like InterMune (NASDAQ:ITMN) is doing, but snake-eyes seem the most likely outcome given the side effects in the study that did work. Faced with the possibility of having to run another phase 3 trial to clear up the mess, Gilead has decided to drop the drug -- better to cut its losses and put energy and cash into its other pipeline drugs.

The loss of darusentan is a major blow to Gilead's diversification away from its HIV franchise. It still has a decent pipeline of non-HIV drugs, but most are in phase 1 or 2 testing, so it'll be quite awhile before HIV drugs aren't the main contributor to Gilead's revenue.

Looking to protect your gains should disaster strike? Todd Wenning shows you one way to do it.