v3.25.2
Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2025
Jul. 23, 2025
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2025  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Trading Symbol SAGE  
Entity Registrant Name Sage Therapeutics, Inc.  
Entity Central Index Key 0001597553  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Title of 12(b) Security Common Stock, par value $0.0001 per share  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Common Stock, Shares Outstanding   62,784,397
Entity Shell Company false  
Entity File Number 001-36544  
Entity Tax Identification Number 27-4486580  
Entity Address, Address Line One 55 Cambridge Parkway  
Entity Address, City or Town Cambridge  
Entity Address, State or Province MA  
Entity Address, Postal Zip Code 02142  
City Area Code 617  
Local Phone Number 299-8380  
Entity Interactive Data Current Yes  
Entity Incorporation, State or Country Code DE  
Document Quarterly Report true  
Document Transition Report false