I am not surprised at all at the price action today. Shorting biotech stocks on FDA approval most of the time makes you money. I can think of a couple examples right away ARNA, VUVS, OREX, KERX, DNDN. There is no imminent upside for MNTA now, making it a good timing for short term investors to exit. MNTA now has ~1.7B market cap it is certainly not cheap.