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 retail drugstore operator China Nepstar Chain Drugstore (NYSE: NPD) sank as much as 11% in early trading today after Goldman Sachs (NYSE: GS) downgraded the stock from neutral to sell.

So what: Goldman's bearish opinion comes on the heels of China Nepstar's disappointing results last week, in which rising operating costs bruised the bottom line. Particularly, Goldman sees a tough operating environment ahead for Chinese retail pharmacies now that the 15% drug mark-up added by hospitals has been eliminated.

Now what: I wouldn't be so quick to pounce on today's plunge. While China Nepstar's growth prospects might be enticing, rising costs and a potentially weakened competitive position are risks that this Fool just isn't willing to take on. Of course, with China Nepstar trading at a clear P/E premium to U.S.-based pharmacies Walgreen (NYSE: WAG) and CVS Caremark (NYSE: CVS), the decision to stay away is that much easier.

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