A regulator's decision drained the market's enthusiasm for the company.The end of the trading week likely can't come fast enough for Vanda Pharmaceuticals (VNDA -6.06%). The commercial-stage biotech's stock took an almost 6% hit on Thursday, following some dispiriting news about one of its investigational drugs. That compared unfavorably to the 1.7% increase in the S&P 500 index during that session.Stomach-disorder drug rejectedBad news about a pipeline product is a fact of life in the biotech and pharmaceu ...