** Brokerage RBC Capital Markets downgrades Biohaven Pharmaceuticals BHVN.N to "sector perform" from "outperform", trims PT to $21 from $54

** New PT still implies a 23.7% upside to the stock's last close

** Shares of BHVN fall 3.8% to $15.4 premarket

** Brokerage says the drugmaker has many promising projects, but also many risks with regard to its pipeline

** Brokerage believes the two projects, troriluzole and Kv7, are crucial for the company's success and flags concerns about troriluzole's chances of getting approved by the FDA

** Co's financial constraints might limit its potential upside, says RBC

** "We are not confident enough in any single one to be able to recommend shares" - RBC

** As of last close, BHVN stock down 57.1% YTD

(Reporting by Padmanabhan Ananthan)

((Padmanabhan.Ananthan@thomsonreuters.com))