Arena Pharmaceuticals (Nasdaq: ARNA) is a clinical-stage biopharmaceutical company focused on developing oral drugs that treat cardiovascular, central nervous system, inflammatory, and metabolic diseases. It currently has one FDA-approved drug to treat obesity, Belviq.

Today, let's look at three things that investors should be watching regarding Arena Pharmaceuticals, as they will provide us with better insight into the company.

1. European Medicines Agency decision
 With Belviq approved by the FDA, Arena has fought about half of the battle. Next on the docket is the review from the Drug Enforcement Agency, which should give investors a better idea of what protocol will need to be undertaken in order to prescribe Belviq, and the big decision by the EMA as to whether Belviq will get a thumbs-up or down in Europe.

Considering that Belviq passed the hurdle of approval in the U.S., it seems likely that the EMA will also approve it as long as the safety profile meets its high standards. Since receiving its 120-day assessment in June, we know that the EMA will make its decision on, or before, Nov. 12. The question now is: Can Belviq become the first drug approved worldwide to treat chronic weight management problems -- and will its marketing partner, Eisai (OTC: ESALY), step up and purchase the company if Belviq gets the nod of approval in the European Union? Arena has already been moving higher on these rumors, and the idea isn't completely far-fetched if the EMA approves Belviq.

2. Safety concerns
 Let's get back to talking about the safety issues soon to be addressed by the DEA review letter. Since the DEA is labeling Belviq as a scheduled drug, it means that there are still safety concerns that will require Arena to complete six additional tests to satisfy the DEA.

First off, it looks like there could be a warning label applied to Belviq saying that it shouldn't be used during pregnancy because of adverse side effects, which could include serotonin syndrome. Don't feel bad, Arena shareholders; VIVUS (Nasdaq: VVUS) -- which just had its obesity drug, Qsymia, approved by the FDA -- will probably also contend with a pregnancy warning as one of its components, topiramate, has been linked to birth defects in the first trimester of pregnancy.

It's also worth noting that the FDA's approval letter didn't mention requiring that an echocardiogram be performed prior to prescribing the drug despite an increase in serotonin-2B levels noted in patients on the drug. This statement will likely result in a warning for those with moderate to severe cardiovascular problems (i.e., heart disease) who are prescribed Belviq. Among Arena's six safety trials, Eisai will be paying to run trials looking at Belviq's effects on heart attacks and strokes. Similarly, Orexigen Therapeutics (Nasdaq: OREX) will be running a cardiovascular safety review on its obesity drug, Contrave.

3. Drug launch
 This is the part where Arena shareholders either hold their breath or gasp in horror. We've seen how big of a nightmare drug launches can be on more than one occasion over the past couple of years. Dendreon's (Nasdaq: DNDN) Provenge prostate cancer treatment was meant to revolutionize treatment and life expectancy for late-stage patients. Instead, sales of the drug limped out of the gate because of its enormous $90,000-plus price tag and physicians' unwillingness to prescribe it on fears that they may not get reimbursed. The recently purchased Human Genome Sciences had the first approved lupus treatment in more than 50 years, and it also failed to launch effectively.

On one side, we can clearly see the advantage of having a premier marketing partner that understands how to launch a drug. Eisai, which holds marketing rights for Belviq in most of North and South America, is one of the world's largest pharmaceutical companies and likely won't have any problem generating sales with its experienced marketing team. On the flip side, having a marketing partner also means that Arena will be sharing its total revenue with Eisai. Don't get me wrong, with Wall Street analysts  having projected peak sales of $2 billion, that still leaves the potential for huge profits, but considering that VIVUS owns Qsymia outright, it could give the profitability edge to VIVUS, assuming it can launch Qsymia effectively.

Foolish roundup
 Now that you know what to watch for, it should be easier to analyze Arena Pharmaceuticals' successes and pitfalls in the future and hopefully give you a leg up on other investors.

If you're still craving even more info on where this company's headed, get your copy of our latest premium research report on Arena Pharmaceuticals. It gives you an in-depth look at opportunities and events that could move Arena's share price and comes with one year of regular updates. Click here to get this report and claim your investing edge.