Shares of VIVUS (Nasdaq: VVUS) hit a 52-week high yesterday. Let's take a look at how it got here to find out whether there are still clear skies ahead.

How it got here
The long road to FDA approval finally made its way to VIVUS' door yesterday. Its anti-obesity drug, now named Qsymia, passed its tests and will now enter into direct competition with Arena Pharmaceuticals' (Nasdaq: ARNA) Belviq. Investors brushed off worries over the drug's dangerous side effects -- particularly its tendency to cause birth defects -- and chose instead to look at the upside.

Although VIVUS has gained a lot in the past year, it's actually on the low end of obesity-drug stock megapops. Orexigen Therapeutics (Nasdaq: OREX) has soundly outperformed VIVUS in the past year, despite being forced to drag out its trials for Contrave at least through next year to counter the FDA's cardiovascular concerns. Arena has been one of the best-performing stocks in the entire market this year, and with only two-thirds of VIVUS' market cap, it might have further still to go.

VVUS Total Return Price Chart

VVUS Total Return Price data by YCharts

Investors have been expecting Qsymia's approval since February, and the one-day megapop that followed the FDA advisory committee's positive recommendation has been responsible for much of the stock's 52-week gains. Can those gains be maintained, or will investors start looking to trim their gains? Let's take a look at a few possibilities.

What you need to know
Anti-obesity drugs and quick-slim compounds have been a chemical holy grail for decades, but a truly effective and riskless solution has proven elusive. Remember Olestra? How about GlaxoSmithKline's alli? If you do, it's probably because of the singularly unpleasant side effects both shared.

Qsymia, thankfully, doesn't appear to have those particular drawbacks. A combination of Johnson & Johnson's (NYSE: JNJ) Topamax, which lost patent protection in 2009, and phentermine -- primarily known as half of the infamous fen-phen weight-loss combination -- Qsymia instead has a benefit-risk profile that combines the characteristics of both drugs. That means users risk heart issues as well as birth defects.

Heart problems aren't exclusive to this drug. Abbott Labs' (NYSE: ABT) Meridia was eventually brought down over cardiovascular concerns, Orexigen's Contrave is already in the thick of that issue, and Belviq's heart-valve data is far from flawless. In the long run, such issues might undermine this entire class of drugs, but for now the benefits far outweigh the risks in investors' minds.

Analysts have given Qsymia a $1.2 billion annual revenue target for 2016, compared to the $1.5 billion Belviq might pull in at its peak, according to Barclays. That still makes Arena's gains look firmer than VIVUS', since profit margins would grant VIVUS a higher hypothetical P/E ratio if their market caps stayed the same.

What's next?
Can VIVUS keep growing? Will Qsymia become a blockbuster? The American lifestyle is not a healthy one, and demand for get-thin-quick schemes is immense. Few obese people, however, are willing to suffer embarrassing or life-threatening side effects just to lose a small amount of weight. The cost of the drugs and the potential for insurance coverage will also factor heavily into the success of any prescription treatment.

Qsymia may also have a tougher time gaining physician buy-in than Arena's new compound, as its formulation simply combines two existing off-patent drugs.

The Motley Fool's CAPS community isn't sure that VIVUS can be a long-term winner. Our members have given the stock a two-star rating, with 73% expecting it to keep growing.

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