There's never a shortage of losers in the stock market.

Let's take a closer look at five of this past week's biggest sinkers.


Sept. 21

Weekly Loss

My Watchlist

Questcor (Nasdaq: QCOR) $30.13 (40%) Add
Horizon Pharmaceuticals (Nasdaq: HZNP) $3.50 (26%) Add
Alpha Natural Resources (NYSE: ANR) $7.21 (16%) Add
Research In Motion (Nasdaq: RIMM) $6.46 (15%) Add
Green Mountain Coffee (Nasdaq: GMCR) $26.76 (14%) Add

Source: Barron's.

Questcor Pharmaceuticals was the Nasdaq's biggest loser, shedding 40% of its value after a major health insurer revealed that it will no longer cover Questcor's flagship drug as a treatment for multiple sclerosis. Even though Questcor points out that the insurer accounts for just 5% of the drug's prescriptions, investors rightfully fear that other insurers will follow suit.

Horizon Pharmaceuticals called in sick after completing a larger-than-expected secondary offering at a steep discount. Raising roughly $75 million through the sale of 21.4 million shares will come in handy for the biotech, but it hurts that it couldn't round up enough buyers without taking down the secondary offering price to $3.50. The stock had closed at $4.58 a day earlier. Ouch!

Alpha Natural Resources tumbled after the country's second-largest coal miner announced that it would be closing several mines and slashing production. Standard & Poor's warned that it may downgrade the company's credit rating.

Research In Motion continued to stumble. A strong iPhone 5 debut, a service outage on Friday, and fears that this week's quarterly report will be brutal weighed on the company behind the once-popular BlackBerry platform.

First Solar was one of the market's biggest winners two weeks ago, but the volatile solar energy bellwether gave back most of those gains a week later. Solar players continue to cut production as global demand softens, and that's weighing on the entire niche.

Ready for a bounce
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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.