Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of drug developer Orexigen Therapeutics (Nasdaq: OREX) spiked today, gaining as much as 22% in intraday trading on heavy volume.

So what: Orexigen issued a press release today saying that it will announce a regulatory update Friday. The announcement will be before the markets open and will be followed by a conference call.

Now what: Above is the entirety of the news out today on Orexigen -- and yet, shares are surging. Why? Obviously investors are guessing that the company will have something positive to say about its diet pill Contrave, which was denied approval by the Food and Drug Administration earlier this year. The future of Contrave is intriguing -- unlike drugs from competitors VIVUS (Nasdaq: VVUS) and Arena Pharmaceuticals (Nasdaq: ARNA), it got a strong nod from a Food and Drug Administration advisory panel -- so it's not too surprising that optimistic investors are still hanging around.

However, the lack of substantive news today means that investors are just assuming what Friday's announcement will bring. And as the saying goes, assuming makes an ... well, you know how it goes.

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or Facebook. The Fool’s disclosure policy prefers dividends over a sharp stick in the eye.