Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the following Registration Statements:

(1) Registration Statement (Form S-8 No. 333-201816) pertaining to the 2014 Equity Incentive Plan, 2015 Equity Incentive Plan and 2015 Employee Stock Purchase Plan of Flex Pharma, Inc.;

(2) Registration Statement (Form S-8 Nos. 333-210283, 333-216534 and 333-223499) pertaining to the 2015 Equity Incentive Plan and 2015 Employee Stock Purchase Plan of Flex Pharma, Inc.;

(3) Registration Statement (Form S-3 No. 333-210289) of Flex Pharma, Inc.; and

(4) Registration Statement (Form S-4 No. 333-229666) of Flex Pharma, Inc.

of our report dated March 6, 2019, with respect to the consolidated financial statements of Flex Pharma, Inc. included in this Annual Report (Form 10-K) of Flex Pharma, Inc. for the year ended December 31, 2018.

/s/ Ernst & Young LLP

Boston, Massachusetts

March 6, 2019