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

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Item 1(a). Name of Issuer:

Avadel Pharmaceuticals plc (the Issuer)

Item 1(b). Address of Issuers Principal Executive Offices:

Block 10-1

Blanchardstown
Corporate Park, Ballycoolin

Dublin 15, Ireland

Item 2(a). Names of Persons Filing:

The names of the persons filing this report (collectively, the Reporting Persons) are:

Perceptive Advisors LLC (Perceptive Advisors)

Joseph Edelman (Mr. Edelman)

Perceptive Life Sciences Master Fund, Ltd. (the Master Fund)

Item 2(b). Address of Principal Business Office or, if None, Residence:

The address of the principal business office of each of the Reporting Persons is:

51 Astor Place, 10th Floor

New
York, NY 10003

Item 2(c). Citizenship:

Perceptive Advisors is a Delaware limited liability company

Mr. Edelman is a United States citizen

The Master Fund is a Cayman Islands corporation

Item 2(d). Title of Class of Securities:

Ordinary shares, nominal value $0.01 per share. (Common Stock)

Item 2(e). CUSIP Number:

05337M 10 4, which represents the CUSIP number for the American Depositary Shares, each representing one share of Common Stock
(ADRs).

Item 3.     If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c),
check whether the person filing is a:

Not applicable.

Item 4.     Ownership.

The information required by this item with respect to each Reporting Person is set forth in Rows 5 through 9 and 11 of the cover page to this
Schedule 13G. The ownership percentages reported are based on 41,435,000 outstanding shares of Common Stock, as reported in the Issuers Form 10-Q filed on August 9, 2017.