Advisory panel rejections carry the greatest clout at the FDA

The FDA is far more likely to be influenced by a rejection than an approval.

Just how influential are those expert FDA advisory panels? Concept Capital studied 120 votes stretching from 2007 to 2010 and found that the agency followed their recommendations three out of four times. But the FDA is far more likely to be influenced by a rejection than an approval. As Forbes' Matthew Herper notes in an analysis, the agency overruled a no vote only three times. Yes turned out to be an easier decision to overlook.

For investors interested in gaming the approval process, Herper looks at the implications of the analysis on the hopes of scoring an upset approval on Vivus' and Arena's weight drugs, both of which went down to defeat recently in front of a committee distinctly leery of a drug category that has been rife with safety issues. "History says the FDA is not likely to change its mind," notes Herper.

Of course, the agency's rejections often come with a set of instructions for changing its decision. Complete response letters can detail new work tha