Shares of Sage Therapeutics Inc. /zigman2/quotes/200179567/composite SAGE +6.65% tumbled 11.2% in premarket trading on Wednesday after Wall Street raised questions about the durability of the experimental treatment for major depressive disorder that Sage is developing with Biogen Inc. /zigman2/quotes/201531540/composite BIIB +4.72% . Biogen's stock was up 0.7% in premarket trading. The companies had announced Monday morning that zuranolone met the primary endpoint in a Phase 3 clinical trial; however, some analysts still have concerns about the commercial appeal of the drug, if it is approved by the Food and Drug Administration. The data demonstrated that there was no statistical difference between giving zuranolone with an antidepressant and an antidepressant with placebo at the 42-day mark. "Some suggestion of near-term durability would be key to broaden commercial uptake of the agent (and perhaps ensure FDA comfort with the consistency of effects across the studies)," RBC Capital Markets analyst Brian Abrahams told investors on Monday. Sage's stock is down 48.4% over the past year, while the broader S&P 500 /zigman2/quotes/210599714/realtime SPX +3.09% is up 15.2%.