Mallinckrodt Announces Reimbursement Approval in Japan for the CELLEX® Extracorporeal Photopheresis (ECP) System for the Treatment of Chronic Graft Versus Host Disease (cGvHD)

– CELLEX ECP is now available for reimbursement in Japan for patients who are steroid-resistant or -intolerant and suffering from cGvHD –

DUBLIN,March 9,2023 -- Mallinckrodt plc,(NYSE American: MNK) ("Mallinckrodt" or the "Company"),a global specialty pharmaceutical company,today announced that Japan's National Health Insurance (NHI) system has approved reimbursement for the CELLEX® extracorporeal photopheresis (ECP) system for the treatment of steroid-resistant or -intolerant chronic graft versus host disease (cGvHD).

"We are very pleased that we have received approval for reimbursement in Japan for the CELLEX ECP System. As a pharmaceutical company focused on improving outcomes for under-served patients with severe and critical conditions,we strive to develop treatment options that address unmet medical needs,"said Masatoyo Gunji,Mallinckrodt General Manager of Japan.

Following the approval of the CELLEX ECP System in Japan in late 2020,with the reimbursement approval,healthcare providers in Japan can now begin to prescribe the CELLEX ECP Systemand treat patients suffering from cGvHD who are steroid-resistant or -intolerant.

The approved uses for the CELLEX ECP System differ depending upon the country. Please refer to each country's Operator's Manuals and labeling for approved uses.

"Chronic graft versus host disease is a highly debilitating disease with a significant impact to the health of these patients with limited treatment options in Japan. The reimbursement approval and subsequent launch of the CELLEX ECP System in Japan represents a crucial milestone that will provide these patients,and their care providers,access to an important therapeutic option where there has been a high unmet medical need," saidLisa French,Executive Vice President and Chief Commercial Officer of Mallinckrodt Pharmaceuticals.

About Chronic Graft Versus Host Disease(cGvHD)

Graft versus host-disease is a common complication of allogeneic hematopoietic stem cell transplantation (HSCT) resulting in significant morbidity and mortality.1 It can be classified as acute or chronic based on the clinical presentation and the time of occurrence after the transplantation. Signs and symptoms of cGvHD nearly always occur within the first year post transplantation but can occasionally happen several years later.2 In cGvHD,the skin is the most frequently affected organ with manifestations of itchy rash,hyper or hypopigmentation and changes in texture2. However,the disease can affect multiple sites,which may have a major impact upon a patient's quality of life.2,3Chronic GvHD can lead to debilitating consequences,such as joint contractures,loss of sight,end-stage lung disease,or mortality resulting from profound chronic immune suppression leading to recurrent or life-threatening infections.1

IMPORTANT SAFETY INFORMATION FOR JAPAN

Intended Use or Efficacy

This system is used as extracorporeal photopheresis therapy in steroid-resistant or -intolerant,chronic graft versus host disease.

Warnings

Directions for Use:

1. When conducting extracorporeal photopheresis therapy for patients receiving other therapy,exercise caution when changing treatment schedules to avoid increased disease activity that may be caused by abrupt withdrawal of previous therapy.

2. Taking into account the condition of the patient,administer an appropriate amount of anticoagulant through the CELLEX device,as thromboembolic events may occur.

Contraindications / Prohibitions

Directions for Use:

1. Do not re-use (Procedural Kit and Methoxsalen Solution).

2. Do not operate the instrument in the presence of flammable anesthetic gases,external radio or electromagnetic disturbances that may interfere with proper performance of the device. There is the risk of ignition and malfunction.

Applicable subject (patient)

Do not use for the following population.

Patients who cannot tolerate extracorporeal volume loss as the patient has possibility of hypotension and shock disease.

Patients exhibiting idiosyncratic reactions to psoralen compounds including methoxsalen,or possessing a specific history of a light-sensitive disease state.

Patients with aphakia because of the significantly increased risk of retinal damage due to the absence of a lens.

Patients possessing a specific history of a disordered coagulation or patients who have had previous splenectomy as anticoagulants is used during therapy.

Patients during pregnancy and lactation as it is likely to cause harm to the unborn child or suckling infant.

Patients who have white blood cell counts greater than 25,000/mm3.

ABOUT THE THERAKOS CELLEX ECP SYSTEM FOR JAPAN

The CELLEX System delivers extracorporeal photopheresis (ECP),and consists of an instrument,procedural kit,methoxsalen solution and a UVA lamp. ECP was initially developed as a therapy for patients with skin symptoms of Cutaneous T-Cell Lymphoma (CTCL).

The CELLEX System was designated as a medical device to be introduced early in Japan by the 15th Study Panel on Early Introduction of Highly Needed Medical Devices. This meeting was organized by the MHLW and held on February 17,2011.

CELLEX was also designated as an orphan medical device by the MHLW on January 18,2017.

APPROVED USES FOR THE THERAKOS CELLEX ECP SYSTEM

The approved uses for CELLEX ECP differ depending upon the country. Please refer to each country's Operator's manuals and labeling for approved uses.

ABOUTMALLINCKRODT

Mallinckrodt is a global business consisting of multiple wholly owned subsidiaries that develop,manufacture,market and distribute specialty pharmaceutical products and therapies. The company's Specialty Brands reportable segment's areas of focus include autoimmune and rare diseases in specialty areas like neurology,rheumatology,hepatology,nephrology,pulmonology,ophthalmology,and oncology; immunotherapy and neonatal respiratory critical care therapies; analgesics; cultured skin substitutes and gastrointestinal products. Its Specialty Generics reportable segment includes specialty generic drugs and active pharmaceutical ingredients. To learn more about Mallinckrodt,visitwww.mallinckrodt.com.

Mallinckrodtuses its website as a channel of distribution of important company information,such as press releases,investor presentations and other financial information. It also uses its website to expedite public access to time-critical information regarding the company in advance of or in lieu of distributing a press release or a filing with theU.S. Securities and Exchange Commission(SEC) disclosing the same information. Therefore,investors should look to the Investor Relations page of the website for important and time-critical information. Visitors to the website can also register to receive automatic e-mail and other notifications alerting them when new information is made available on the Investor Relations page of the website.

CAUTIONARY STATEMENTS RELATED TO FORWARD-LOOKING STATEMENTS

This release contains forward-looking statements,including concerning the use of the CELLEX System including potential benefits associated with its use. The statements are based on assumptions about many important factors,including the following,which could cause actual results to differ materially from those in the forward-looking statements: satisfaction of regulatory and other requirements; actions of regulatory bodies and other governmental authorities; changes in laws and regulations; issues with product quality,manufacturing or supply,or patient safety issues; and other risks identified and described in more detail in the "Risk Factors" section ofMallinckrodt'smost recent Annual Report on Form 10-K and other filings with theSEC,all of which are available on its website. The forward-looking statements made herein speak only as of the date hereof andMallinckrodtdoes not assume any obligation to update or revise any forward-looking statement,whether as a result of new information,future events and developments or otherwise,except as required by law.

CONTACT

Media Inquiries

Heather Guzzi

Green Room Communications

+1 973-524-4112

hguzzi@greenroompr.com

Investor Relations

Daniel J. Speciale,CPA

Vice President,Finance and Investor Relations Officer

+1 314-654-3638

daniel.speciale@mnk.com

Mallinckrodt Pharma K.K.

Junichi Yoshimura

Sales & Marketing,Product Manager

+81 3 6441 3604

junichi.yoshimura@mnk.com

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© 2023Mallinckrodt.JP-2300001 3/23

References

1 Filipovich. Biol Blood Marrow Transplant. 2005; 11:945–956.

2 Jagasia. Biol Blood Marrow Transplant. 2015; 21(3): 389–401.

3 Pavletic,et al. Biol Blood Marrow Transplant. 2006;12:252–66.

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