v3.19.1
Document and Entity Information
12 Months Ended
Dec. 31, 2018
Document And Entity Information [Abstract]  
Entity Registrant Name Flex Pharma, Inc.
Amendment Description Amendment No. 1
Entity Central Index Key 0001615219
Entity Filer Category Non-accelerated Filer
Entity Small Business true
Entity Emerging Growth Company true
Entity Ex Transition Period true
Document Type S-4/A
Document Period End Date Dec. 31, 2018
Amendment Flag true