13G Filing: Perceptive Advisors and Avadel Pharmaceuticals PLC (AVDL)

Page 8 of 8

Page 8 of 8 – SEC Filing


EXHIBIT 1

AGREEMENT

The persons below hereby agree that
the Schedule 13G to which this agreement is attached as an exhibit, as well as all future amendments to such Schedule 13G, shall be filed on behalf of each of them. This agreement is intended to satisfy the requirements of Rule 13d-1(k)(1)(iii)
under the Securities Exchange Act of 1934.

Date: November 9, 2017

PERCEPTIVE ADVISORS LLC
By: /s/ Joseph Edelman

Name: Joseph Edelman

Title: Managing
Member

/s/ Joseph Edelman

JOSEPH EDELMAN

PERCEPTIVE LIFE SCIENCES MASTER FUND, LTD.
By: Perceptive Advisors LLC
By: /s/ Joseph Edelman

Name: Joseph Edelman

Title: Managing
Member

Follow Avadel Pharmaceuticals Plc (NASDAQ:AVDL)

Page 8 of 8