What's better than momentum? Mo' momentum.

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

Company

May 11 Weekly Gain My Watchlist
Arena Pharmaceuticals (Nasdaq: ARNA) $6.36 146% Add
Vertex Pharmaceuticals (Nasdaq: VRTX) $62.02 66% Add
Rosetta Stone (NYSE: RST) $13.64 29% Add
Accretive Health (NYSE: AH) $10.86 27% Add
Achillion Pharmaceuticals (Nasdaq: ACHN) $7.20 20% Add

Source: Barron's.

Arena Pharmaceuticals was last week's biggest winner, soaring 146% after an advisory committee showed support for its lorcaserin weight-loss treatment. Several obesity drugs are battling it out for regulatory approval, and the stocks themselves will pack on the pounds or shed them as the victors emerge.

The market's second biggest gainer was another biotech. Vertex rose in a sluggish market after releasing promising clinical data for its VX-809 and Kalydeco drugs in the treatment of cystic fibrosis.

Rosetta Stone investors know that applause doesn't need a translation. The language learning program company posted stronger-than-expected quarterly results. Revenue soared above estimates, and Rosetta Stone posted a much smaller deficit than what Wall Street was targeting.

Accretive Health may have slashed its outlook, but analysts preferred to focus on the health care services provider's ability to surpass market expectations in its latest quarter.

Finally we have Achillion moving higher after reporting a narrowing quarterly deficit, offering up encouraging development news, and snagging a UBS analyst upgrade.

More winners for you
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The Motley Fool owns shares of Rosetta Stone. Motley Fool newsletter services have recommended buying shares of Vertex Pharmaceuticals and Rosetta Stone. The Motley Fool has a disclosure policy. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days.

Longtime Fool contributor Rick Munarriz calls them as he sees them. He does not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.