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.

Good morning, fellow Foolish investors! It's time to check in on the top stories in the health care sector this morning.

Arena gaining momentum?
Shares of obesity drugmaker Arena Pharmaceuticals (NASDAQ:ARNA) are up another 3% in premarket trading today following yesterday's 5.27% gain. This latest rally in Arena appears to be driven by a couple of factors. Firstly, Arena recently submitted a marketing application for Belviq in Brazil as a treatment for chronic weight management. Secondly, Belviq saw slightly improving prescription numbers in the U.S. last week. And perhaps most importantly, Arena Pharmaceuticals and its marketing partner Eisai (NASDAQOTH: ESALY) have successfully convinced CVS Caremark and Aetna to include the drug in their coverage, which could provide a major boost to sales going forward.  

Should you join the party? Taking a long-term view, I think it's best to stay on the sidelines for now. Arena and Eisai still have a ways to go to make Belviq a major revenue generator, and there's no way of knowing how Orexigen Therapeutic's (NASDAQ:OREX) Contrave will affect Belviq sales, if the drug gains approval later this year.

That said, I like the fact that things are unfolding according to Eisai's marketing plan stated awhile back, showing the two companies are dedicated to overcoming the significant hurdles associated with marketing an obesity drug. So, stay tuned!

Chelsea hopes for a sweet Valentine's gift from the FDA
Perhaps one of the most watched stories in health care today will be Chelsea Therapeutics (NASDAQ:CHTP) and the forthcoming regulatory decision for its experimental drug Northera, indicated as a treatment for neurogenic orthostatic hypotension. Northera previously received a strong endorsement from the FDA Advisory Committee, but the FDA reviewer appeared to be less than enthusiastic about the drug's clinical trials. So, there is still an inkling of doubt about the drug's approval today, despite a 16 to 1 'yes' vote from the Advisory Committee. 

Investors are also concerned that the drug's label could limit its use to 1-2 weeks, or the FDA could require a particularly burdensome postmarketing study requirement. Indeed, there are several unknowns surrounding Chelsea and Northera this morning. And this is why I think it's best to take a pass on Chelsea for the time being.

Even so, I think you should keep Chelsea on your watch list. If the drug is approved today, the company could be dramatically undervalued, depending on how the label turns out. 

Biopharmas like Arena and Chelsea have been strong performers lately, but this stock may be a better pick going forward.
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George Budwell owns shares of Orexigen Therapeutics. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.