SUPPORT AGREEMENT

Exhibit 10.1

SUPPORT AGREEMENT

This SUPPORT AGREEMENT (“Agreement”), executed as a Deed, is made and entered into as of April 23, 2014, by and among Mallinckrodt plc, an Irish public limited company (the “Company”) and Paulson & Co. Inc. on behalf of itself and of all funds and accounts managed by Paulson & Co. Inc. or any of its affiliates, each of which shall be deemed to be a party and signatory hereto (each a “Shareholder” and collectively the “Shareholders”).

WITNESSETH:

WHEREAS, on April 5, 2014, the Company, Quincy Merger Sub, Inc. and Questcor Pharmaceuticals, Inc. (“Questcor”) entered into an Agreement and Plan of Merger (as it may be modified, amended, supplemented or waived, the “Merger Agreement”);

WHEREAS, on June 28, 2013, the Company and Computershare Trust Company, N.A., as rights agent (the “Rights Agent”), entered into the Rights Agreement (the “Rights Agreement”);

WHEREAS, concurrently with the execution of this Agreement, the Company and the Rights Agent are amending the Rights Agreement by entering into an Amendment to the Rights Agreement (the “Rights Agreement Amendment”) in the form attached as Exhibit A hereto;

NOW, THEREFORE, in consideration of the foregoing and the mutual promises, representations, warranties, covenants and agreements of the parties contained herein and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged by each of the parties hereto, the parties hereto, intending to be legally bound hereby, agree as follows:

ARTICLE 1

VOTING

-2-

ARTICLE 2

COVENANTS

-3-

-4-

ARTICLE 3

REPRESENTATIONS AND WARRANTIES

The Shareholders, jointly and severally, represent and warrant to the Company as follows:

-5-

The Company represents and warrants to the Shareholders as follows:

ARTICLE 4

TERM

This Agreement shall remain in full force and effect until the later of (a) eighteen (18) months after the date hereof and (b) such time as the Shareholders Beneficially Own less than ten percent (10%) of Ordinary Shares then outstanding.

Article 4 shall survive the expiration of this Agreement. The expiration of this Agreement shall not relieve any party hereto from liability for any breach of this Agreement prior to such expiration.

ARTICLE 5

GENERAL

All notices, requests, claims, demands and other communications hereunder shall be in writing and shall be deemed to have been duly given to a party if delivered in person or sent by overnight delivery (providing proof of delivery) to the party at the following addresses (or at such other address for a party as shall be specified by like notice) on the date of delivery, or if by facsimile, upon confirmation of receipt:

-6-

If to the Company:

with a copy (which shall not constitute notice) to:

If to the Shareholders:

with a copy (which shall not constitute notice) to

Nothing in this Agreement, whether express or implied, is intended to or shall confer any rights, benefits or remedies under or by reason of this Agreement on any persons other than the parties hereto, nor is anything in this Agreement intended to relieve or discharge the obligation or liability of any third persons to any party.

-7-

This Agreement and any dispute arising out of or in connection with it or its subject matter or formation (including non-contractual disputes or claims) shall be governed by and construed in accordance with the laws of Ireland and each Shareholder agrees that the courts of Ireland and the courts located in the City of New York in the State of New York are to have jurisdiction to hear and determine any suit, action or proceedings that may arise out of or in connection with this Agreement and, for such purposes, each Shareholder irrevocably submits to the jurisdiction of such courts.

This Agreement shall be binding upon and inure to the benefit of and be enforceable only by the parties hereto and their respective permitted assigns. None of the Shareholders may assign its rights or delegate its obligations under this Agreement, whether by operation of law or otherwise.

This Agreement may only be amended pursuant to a written agreement executed by all the parties, and no waiver of compliance with any provision or condition of this Agreement and no consent provided for in this Agreement shall be effective unless evidenced by a written instrument executed by the party against whom such waiver or consent is to be effective. No failure or delay by a party in exercising any right, power or privilege hereunder shall operate as a waiver thereof, nor shall any single or partial exercise thereof preclude any other or further exercise thereof or the exercise of any right, power or privilege hereunder.

This Agreement constitutes the entire agreement of all the parties and supersedes any and all prior and contemporaneous agreements, memoranda, arrangements and understandings, both written and oral, between the parties, or any of them, with respect to the subject matter hereof. No representation, warranty, promise, inducement or statement of intention has been made by any party which is not contained in this Agreement and no party shall be bound by, or be liable for, any alleged representation, promise, inducement or statement of intention not contained herein. The parties expressly disclaim reliance on any information, statements, representations or warranties regarding the subject matter of this Agreement other than the terms of this Agreement.

This Agreement may be executed in any number of counterparts (including by facsimile transmission), each of which shall be deemed to be an original, but all of which together shall constitute one binding agreement on the parties, notwithstanding that not all parties are signatories to the same counterpart.

-8-

All attorneys’ fees, costs and expenses incurred in connection with this Agreement and all matters related hereto will be paid by the party incurring such fees, costs or expenses.

The captions contained in this Agreement are for convenience only and shall not affect the construction or interpretation of any provisions of this Agreement.

If any term, provision, covenant or restriction of this Agreement is held by a court of competent jurisdiction or other authority to be invalid, void or unenforceable, the remainder of the terms, provisions, covenants and restrictions of this Agreement shall remain in full force and effect and shall in no way be affected, impaired or invalidated.

Each Shareholder has been given a realistic opportunity to consider whether or not it should enter into this Agreement and give the undertakings contained herein and it has received independent advice about the nature of this Agreement and the undertakings contained herein. Without prejudice to any other rights or remedies which the Company may have, each Shareholder acknowledges and agrees that damages would not be an adequate remedy for any breach by it of any of its obligations under this Agreement and that the Company shall be entitled (in addition to damages) to the remedies of injunction, specific performance and other equitable relief for any threatened or actual breach of any of its obligations under this Agreement and no proof of special damages shall be necessary for the enforcement by the Company of any of the Company’s rights hereunder, and each Shareholder further agrees to waive any requirement for the security or posting of any bond in connection with such remedy or relief.

With regard to any of Ordinary Shares and/or shares of Questcor Common Stock (as applicable) which are not registered in the name of a Shareholder, each Shareholder undertakes to take all steps reasonably necessary to procure the compliance by the registered holder or holders of such Ordinary Shares and/or shares of Questcor Common Stock (as applicable) with the undertakings, agreements and obligations of whatsoever nature contained in this Agreement, as and to the extent necessary to effect such undertakings, agreements and obligations. Each Shareholder shall cause each other Shareholder to comply with such other Shareholder’s undertakings, agreements and obligations in this Agreement.

[Remainder of Page Intentionally Left Blank; Signature Page Follows]

-9-

IN WITNESS WHEREOF, the parties have duly executed this Agreement as a deed of the date first above written.

GIVEN under the common seal of

MALLINCKRODT PUBLIC LIMITED COMPANY

and DELIVERED as a DEED

[Signature Page to the Support Agreement]

[Signature Page to the Support Agreement]

Exhibit A

AMENDMENT TO THE RIGHTS AGREEMENT

This AMENDMENT TO THE RIGHTS AGREEMENT (this “Amendment”), executed as a Deed Poll, is made and entered into as of April 23, 2014, between Mallinckrodt plc, an Irish public limited company (the “Company”), and Computershare Trust Company, N.A., as rights agent (the “Rights Agent”). All capitalized terms used in this Amendment and not defined herein shall have the meanings ascribed thereto in the Rights Agreement.

WHEREAS, the Company and the Rights Agent have entered into that certain Rights Agreement, dated as of June 28, 2013 (the “Rights Agreement”);

WHEREAS, on April 5, 2014, the Company, Quincy Merger Sub, Inc. and Questcor Pharmaceuticals, Inc. entered into an Agreement and Plan of Merger (as it may be modified, amended, supplemented or waived, the “Merger Agreement”);

WHEREAS, concurrently with the execution of this Amendment, the Company and Paulson & Co. Inc., on behalf of itself and of all funds and accounts managed by Paulson & Co. Inc. or any of its affiliates (collectively, “Paulson”) have entered into a Support Agreement (the “Support Agreement”);

WHEREAS, pursuant to Section 27 of the Rights Agreement, at any time prior to the time at which any Person becomes an Acquiring Person, the Company may supplement or amend the Rights Agreement without the approval of any holders of Right Certificates in order to make any provisions with respect to the Rights which the Company may deem necessary or desirable, any such supplement or amendment to be evidenced by a writing signed by the Company and the Rights Agent;

WHEREAS, the Board of Directors of the Company desires to amend the Rights Agreement to modify the definition of “Acquiring Person” with respect to Paulson only in consideration for Paulson’s entry into the Support Agreement;

WHEREAS, no person has yet become an Acquiring Person and, subject to and in accordance with the terms of this Amendment, the Company has directed and the Rights Agent has agreed to amend the Rights Agreement in certain respects, as more particularly set forth herein.

NOW, THEREFORE, in consideration of these premises and the mutual covenants and agreements set forth in the Rights Agreement and this Amendment, the parties hereto agree to modify the Rights Agreement as set forth below.

1.1 Section 1 of the Rights Agreement is hereby amended and supplemented to include the following definitions in the appropriate locations, with the subsequent definitions being appropriately re-lettered and cross-references thereto being appropriately revised:

““Effective Time” shall have the meaning set forth in the Merger Agreement.”

““Merger Agreement” shall mean the Agreement and Plan of Merger, dated as of April 5, 2014, by and among the Company, Quincy Merger Sub, Inc. and Questcor Pharmaceuticals, Inc. (as such agreement is amended or supplemented from time to time).”

““Paulson” shall mean, collectively, Paulson & Co. Inc. and all funds and accounts managed by Paulson & Co. Inc. or any of its affiliates.”

““Qualified Institutional Investor” shall mean, as of any time of determination, a Person that is described in Rule 13d-1(b)(1) or Rule 13d-1(c) promulgated under the Exchange Act and is eligible to report (and, if such Person is the Beneficial Owner of greater than 5% of the Ordinary Shares of the Company, does in fact report) beneficial ownership of Ordinary Shares of the Company on Schedule 13G, and is not required to file a Schedule 13D (or any successor or comparable report) with respect to Ordinary Shares of the Company.”

1.2 Section 1(a) of the Rights Agreement is hereby amended and restated in its entirety so that it shall read as follows:

““Acquiring Person” shall mean any Person who or which, together with all Affiliates and Associates of such Person, shall be the Beneficial Owner of 10% or more of the Ordinary Shares of the Company then outstanding, but shall not include the Company, any Subsidiary of the Company, any employee benefit plan of the Company or any Subsidiary of the Company, or any entity holding Ordinary Shares for or pursuant to the terms of any such plan. Notwithstanding the foregoing, no Person shall become an “Acquiring Person” as the result of an acquisition of Ordinary Shares by the Company which, by reducing the number of Ordinary Shares of the Company outstanding, increases the proportionate number of Ordinary Shares of the Company Beneficially Owned by such Person to 10% or more of the Ordinary Shares of the Company then outstanding; provided, however, that, if a Person shall become the Beneficial Owner of 10% or more of the Ordinary Shares of the Company then outstanding by reason of share purchases by the Company and shall, after such share purchases by the Company, become the Beneficial Owner of any additional Ordinary Shares of the Company, then such Person shall be deemed to be an “Acquiring Person.” Notwithstanding the foregoing, if the Board of Directors of the Company determines in good faith that a Person who would otherwise be an “Acquiring Person,” as defined pursuant to the foregoing provisions of this paragraph (a), has become such inadvertently, and such Person divests as promptly as practicable a sufficient number of Ordinary Shares so that such Person would no longer be an “Acquiring Person,” as defined pursuant to the foregoing provisions of this paragraph (a), then such Person shall not be deemed to be an “Acquiring Person” for any purposes of this Agreement. Notwithstanding the foregoing, if a bona fide swaps dealer who would otherwise be an “Acquiring Person” has become so as a result of its actions in the ordinary course of its business that the Board of Directors of the Company determines, in its sole discretion, were taken without the intent or effect of evading or assisting any other Person to evade the purposes and intent of this Agreement, or otherwise seeking to control or influence the management or policies of the Company, then, and unless and until the Board of Directors shall otherwise determine, such Person shall not be deemed to be an “Acquiring Person” for any purposes of this Agreement. Notwithstanding the foregoing, references to “10%” in this definition of Acquiring Person, with respect to Paulson only and not with respect to any other Person shall be deemed to be replaced with references to 20% (the “Paulson Acquiring Person Threshold”); provided, however, that if the Merger Agreement is terminated in accordance with its terms prior

-2-

to the Effective Time, the Paulson Acquiring Person Threshold shall thereupon become the lesser of (x) 20% and (y) 0.0001% plus the percentage of Ordinary Shares of the Company Beneficially Owned by Paulson at the time of such termination; provided, further, that if the Effective Time occurs, the Paulson Acquiring Person Threshold shall immediately following the Effective Time become the greater of (x) 10% and (y) 0.0001% plus the percentage of Ordinary Shares of the Company Beneficially Owned by Paulson immediately following the Effective Time as a result of its Beneficial Ownership of Ordinary Shares of the Company (not in excess of the Paulson Acquiring Person Threshold) immediately prior to the Effective Time; provided, further, however, that if at any time following such termination or the Effective Time, as the case may be, the percentage of Ordinary Shares of the Company Beneficially Owned by Paulson decreases, the Paulson Acquiring Person Threshold shall thereupon be reduced to 0.0001% plus the percentage of Ordinary Shares of the Company Beneficially Owned by Paulson following such decrease in Beneficial Ownership; provided, further, however, that in no event will the Paulson Acquiring Person Threshold be less than 10%; provided, further, however, that this sentence shall apply only for so long as Paulson is a Qualified Institutional Investor.”

2.1 Exhibit B of the Rights Agreement is hereby amended and supplemented by inserting in the first paragraph following the words “dated as of June 28, 2013” the words “, as amended as of April 23, 2014”.

3.1 Exhibit C of the Rights Agreement is hereby amended and supplemented to add the following after the sixth paragraph thereof:

“Notwithstanding the foregoing, under certain circumstances described in the Rights Agreement, references to 10% above will mean, with respect to Paulson & Co. Inc. and all funds and accounts managed by Paulson & Co. Inc. or any of its affiliates only, 20% or less (but not less than 10%).”

Except as specifically amended and supplemented hereby, all terms, covenants and conditions of the Rights Agreement as heretofore in effect shall remain in full force and effect and are hereby ratified and confirmed in all respects.

This Amendment and any dispute arising out of or in connection with it or its subject matter or formation (including non-contractual rights disputes or claims) shall be deemed to be a contract made under the laws of Ireland and for all purposes shall be governed by and construed in accordance with the laws of Ireland applicable to contracts to be made and performed entirely within Ireland, except that the rights, duties and obligations of the Rights Agent shall be governed by and construed in accordance with the laws of the state of New York.

-3-

This Amendment may be executed in any number of counterparts and each of such counterparts shall for all purposes be deemed to be an original, and all such counterparts together shall constitute but one and the same instrument. A signature to this Amendment transmitted electronically shall have the same authority, effect and enforceability as an original signature.

[Remainder of Page Intentionally Left Blank]

-4-

IN WITNESS WHEREOF, the parties have executed this Amendment as a deed with the intention that it be delivered on the date first written above.

[Signature Page to the Amendment to the Rights Agreement]