Shares of Acadia Pharmaceuticals Inc. /zigman2/quotes/205236646/composite ACAD +2.69% plunged 42.1% to pace all premarket decliners Tuesday, in the wake of the company's announcement that the Food and Drug Administration found undisclosed deficiencies in its supplemental New Drug Application (NDA) for pimavanserin, a treatment for hallucinations and delusions associated with dementia-related psychosis. The company said late Monday that the FDA's identification of deficiencies precluded discussion of labeling and post-marketing requirements. But the FDA did not specify the deficiencies it identified, Acadia said. That led Raymond James analyst Danielle Brill to downgrade Acadia to outperform from strong buy and slash the price target to $35 from $65. "We have no good guesses as to what 'deficiencies' the FDA found, but one thing is clear -- the regulatory outlook for DRP suddenly appears quite dire," Brill wrote in a note to clients. Stifel Nicolaus's Paul Matteis cut his rating to hold from buy and his price target to $27 from $68. "Not defending the stock on weakness; DRP prospects seem bleak, tough for us to be confident," Matteis wrote. The stock, which is on track to open at the lowest price seen during regular-session hours since September 2019, has lost 12.5% over the past three months through Monday, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +2.43% has gained 4.0%.