Commitments and Contingencies	3 Months Ended
Mar. 31, 2026
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. Commitments and contingencies Indemnification agreements In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. In accordance with the Articles of Association, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving at the Company’s request in such capacity. There have been no claims to date, and the Company has director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims. Novartis Asset Purchase Agreements The Company has agreed to make future payments to Novartis comprising amounts equal to ascending specified percentages of tiered annual worldwide net sales (beginning at high single digits and reaching into double digits at higher sales) of products that include the assets acquired. The levels of ascending percentages of tiered annual worldwide net sales are stipulated under the respective Purchase Agreements. The Company further agreed that in the event it transfers, licenses, assigns or leases all or substantially all of its assets, it will pay Novartis a percentage of the proceeds of such transaction, subject to certain deductions. The payment of a percentage of proceeds is not payable with respect to any transaction involving equity interests of Mereo BioPharma Group plc, a merger or consolidation of Mereo BioPharma Group plc, or a sale of any assets of Mereo BioPharma Group plc. License agreement with AstraZeneca In October 2017, the Company entered into an exclusive license and option agreement (the “AstraZeneca License Agreement”) and subscription deed (the “AstraZeneca Subscription Deed”), together (the “Original Agreements”) with AstraZeneca AB (“AstraZeneca”). Each of these were amended on November 8, 2024, when the Company entered into an amendment and restatement agreement related to the AstraZeneca License Agreement (the “Amended AstraZeneca License Agreement”) and a Deed of Amendment and Restatement related to the AstraZeneca Subscription Deed (the “Amended AstraZeneca Subscription Deed”) together (the “Amended AstraZeneca Agreements”). Under the terms of the Original Agreements, the Company obtained from AstraZeneca an exclusive worldwide, sub-licensable license under AstraZeneca’s intellectual property rights relating to alvelestat, with an option to acquire such intellectual property rights following commencement of a pivotal trial and payment of related milestone payments, together with the acquisition of certain related assets. Upon entering into the Original Agreements, the Company made a payment of $3.0 million and issued 490,798 ordinary shares (equivalent to 98,159 ADSs) to AstraZeneca, for an aggregate upfront payment equal to $5.0 million. Upon execution of the Amended AstraZeneca License Agreement, the Company issued 2,044,390 ordinary shares and paid $0.5 million to AstraZeneca in respect of an agreed milestone. Under the terms of the Amended AstraZeneca Agreements, the Company has agreed, in connection with certain further development and regulatory milestones, to make potential future payments both in cash and through the issue of a variable number of additional ADSs to AstraZeneca of up to $114.3 million in the aggregate for products included in the Amended AstraZeneca License Agreement. The number of ADSs to be issued to satisfy each equity milestone is determined by dividing a monetary amount by a defined subscription price based on the weighted average trading price of the Company's ADSs, and the obligation is presented as a liability under ASC Topic 480, Distinguishing Liabilities from Equity. The Company continues to reassess the fair value of such instruments in each reporting period until the milestones are achieved, if ever, and the issuance of shares occurs. Given the pervasive uncertainty involved in establishing the amounts, timing and likelihood of the future cash flows, including the Company’s ability to secure either a partnership or alternative forms of non-dilutive financing, the possible terms and rate of such a partnership or financing, the clinical and regulatory performance of the product candidate and the lack of comparable recent transactions, the Company has determined the fair value of the equity milestones to be paid in a variable number of shares pursuant to its Amended AstraZeneca License Agreement to be negligible and therefore assigned a nil value to the instrument as of March 31, 2026 and December 31, 2025. In addition to the development and regulatory milestones, the Company has agreed to make payments to AstraZeneca based on specified commercial milestones of the product. The Company has also agreed to pay a specified percentage of sub-licensing revenue to AstraZeneca and to make royalty payments to AstraZeneca equal to ascending specified percentages of tiered annual worldwide net sales by the Company of licensed products (subject to certain reductions), ranging from the high single digits to low double digits. Royalties will be payable on a licensed-product-by-licensed-product and country-by-country basis until the later of ten years after the first commercial sale of such licensed product in such country and expiration of the last patent covering such licensed product in such country that would be sufficient to prevent generic entry. The Company has agreed to use commercially reasonable efforts to develop and commercialize at least one licensed product. The Amended AstraZeneca License Agreement will expire on the expiration of the last-to-expire royalty term with respect to all licensed products. Upon the expiration of the royalty term for a licensed product in a particular country, the licenses to the Company for such product in such country will become fully paid and irrevocable. Prior to exercise of the Option, if at all, the Company may terminate the Amended AstraZeneca License Agreement upon prior written notice. Either party may terminate the agreement upon prior written notice for the other party’s material breach that remains uncured for a specified period of time or insolvency. Research and development activities The Company enters into contracts in the normal course of business with contract research organizations (“CROs”), contract manufacturing organizations (“CMOs”) and other third parties to assist in the performance of research and development activities and other services and products for operating purposes. The contracts with CROs generally provide for termination on notice, and therefore, are cancellable contracts and not included herein. The Company had no manufacturing commitments with CMOs as of March 31, 2026 and December 31, 2025. Manufacturing and supply agreement with Ultragenyx In December 2024, the Company entered into a manufacturing and supply agreement with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”) under which Ultragenyx is responsible for the manufacture and supply of setrusumab to the Company in its territories. The Company is also required to reimburse Ultragenyx for a portion of the manufacturing process development costs, future commercial supply costs as well as a portion of costs in the event of cancellation of certain manufacturing slots. Pursuant to this agreement, the Company has recognized $2.3 million for its share of the costs related to cancellation of certain manufacturing slots by Ultragenyx in the three months ended March 31, 2026. Any additional payments are subject to our agreement and cannot currently be estimated. Legal proceedings Putative Securities Class Action On February 4, 2026, a putative class action complaint was filed in the United States District Court for the Southern District of New York against the Company, its Chief Executive Officer, Denise Scots-Knight, and its Chief Scientific Officer, John Lewicki (the “Defendants”). This action, captioned Dodge v. Mereo Biopharma Group PLC (No. 1:26-cv-988), alleges that the Defendants violated federal securities law by making false and misleading statements regarding the Company's business and operations. The Plaintiff seeks the payment of damages allegedly sustained by her and the putative class by reason of the allegations set forth in the complaint, plus interest, and legal and other costs and fees. On April 29, 2026, the court appointed a lead plaintiff and lead counsel. No responsive pleadings have been filed to date. The Company intends to vigorously defend against this action, but at this early stage, the Company can neither predict the ultimate outcome, nor estimate any range of possible losses. From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. Except for the abovementioned putative securities class action, the Company was not a party to any material litigation and did not have any material contingency reserves established for any liabilities as of March 31, 2026 and December 31, 2025.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2026

Commitments and Contingencies Disclosure [Abstract]

14. Commitments and contingencies

Indemnification agreements

In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. In accordance with the Articles of Association, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving at the Company’s request in such capacity. There have been no claims to date, and the Company has director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims.

Novartis Asset Purchase Agreements

The Company has agreed to make future payments to Novartis comprising amounts equal to ascending specified percentages of tiered annual worldwide net sales (beginning at high single digits and reaching into double digits at higher sales) of products that include the assets acquired. The levels of ascending percentages of tiered annual worldwide net sales are stipulated under the respective Purchase Agreements.

The Company further agreed that in the event it transfers, licenses, assigns or leases all or substantially all of its assets, it will pay Novartis a percentage of the proceeds of such transaction, subject to certain deductions. The payment of a percentage of proceeds is not payable with respect to any transaction involving equity interests of Mereo BioPharma Group plc, a merger or consolidation of Mereo BioPharma Group plc, or a sale of any assets of Mereo BioPharma Group plc.

License agreement with AstraZeneca

In October 2017, the Company entered into an exclusive license and option agreement (the “AstraZeneca License Agreement”) and subscription deed (the “AstraZeneca Subscription Deed”), together (the “Original Agreements”) with AstraZeneca AB (“AstraZeneca”). Each of these were amended on November 8, 2024, when the Company entered into an amendment and restatement agreement related to the AstraZeneca License Agreement (the “Amended AstraZeneca License Agreement”) and a Deed of Amendment and Restatement related to the AstraZeneca Subscription Deed (the “Amended AstraZeneca Subscription Deed”) together (the “Amended AstraZeneca Agreements”).

Under the terms of the Original Agreements, the Company obtained from AstraZeneca an exclusive worldwide, sub-licensable license under AstraZeneca’s intellectual property rights relating to alvelestat, with an option to acquire such intellectual property rights following commencement of a pivotal trial and payment of related milestone payments, together with the acquisition of certain related assets. Upon entering into the Original Agreements, the Company made a payment of $3.0 million and issued 490,798 ordinary shares (equivalent to 98,159 ADSs) to AstraZeneca, for an aggregate upfront payment equal to $5.0 million. Upon execution of the Amended AstraZeneca License Agreement, the Company issued 2,044,390 ordinary shares and paid $0.5 million to AstraZeneca in respect of an agreed milestone.

Under the terms of the Amended AstraZeneca Agreements, the Company has agreed, in connection with certain further development and regulatory milestones, to make potential future payments both in cash and through the issue of a variable number of additional ADSs to AstraZeneca of up to $114.3 million in the aggregate for products included in the Amended AstraZeneca License Agreement.

The number of ADSs to be issued to satisfy each equity milestone is determined by dividing a monetary amount by a defined subscription price based on the weighted average trading price of the Company's ADSs, and the obligation is presented as a liability under ASC Topic 480, Distinguishing Liabilities from Equity. The Company continues to reassess the fair value of such instruments in each reporting period until the milestones are achieved, if ever, and the issuance of shares occurs. Given the pervasive uncertainty involved in establishing the amounts, timing and likelihood of the future cash flows, including the Company’s ability to secure either a partnership or alternative forms of non-dilutive financing, the possible terms and rate of such a partnership or financing, the clinical and regulatory performance of the product candidate and the lack of comparable recent transactions, the Company has determined the fair value of the equity milestones to be paid in a variable number of shares pursuant to its Amended AstraZeneca License Agreement to be negligible and therefore assigned a nil value to the instrument as of March 31, 2026 and December 31, 2025.

In addition to the development and regulatory milestones, the Company has agreed to make payments to AstraZeneca based on specified commercial milestones of the product. The Company has also agreed to pay a specified percentage of sub-licensing revenue to AstraZeneca and to make royalty payments to AstraZeneca equal to ascending specified percentages of tiered annual worldwide net sales by the Company of licensed products (subject to certain reductions), ranging from the high single digits to low double digits. Royalties will be payable on a licensed-product-by-licensed-product and country-by-country basis until the later of ten years after the first commercial sale of such licensed product in such country and expiration of the last patent covering such licensed product in such country that would be sufficient to prevent generic entry. The Company has agreed to use commercially reasonable efforts to develop and commercialize at least one licensed product.

The Amended AstraZeneca License Agreement will expire on the expiration of the last-to-expire royalty term with respect to all licensed products. Upon the expiration of the royalty term for a licensed product in a particular country, the licenses to the Company for such product in such country will become fully paid and irrevocable. Prior to exercise of the Option, if at all, the Company may terminate the Amended AstraZeneca License Agreement upon prior written notice. Either party may terminate the agreement upon prior written notice for the other party’s material breach that remains uncured for a specified period of time or insolvency.

Research and development activities

The Company enters into contracts in the normal course of business with contract research organizations (“CROs”), contract manufacturing organizations (“CMOs”) and other third parties to assist in the performance of research and development activities and other services and products for operating purposes. The contracts with CROs generally provide for termination on notice, and therefore, are cancellable contracts and not included herein. The Company had no manufacturing commitments with CMOs as of March 31, 2026 and December 31, 2025.

Manufacturing and supply agreement with Ultragenyx

In December 2024, the Company entered into a manufacturing and supply agreement with Ultragenyx Pharmaceutical Inc. (“Ultragenyx”) under which Ultragenyx is responsible for the manufacture and supply of setrusumab to the Company in its territories. The Company is also required to reimburse Ultragenyx for a portion of the manufacturing process development costs, future commercial supply costs as well as a portion of costs in the event of cancellation of certain manufacturing slots. Pursuant to this agreement, the Company has recognized $2.3 million for its share of the costs related to cancellation of certain manufacturing slots by Ultragenyx in the three months ended March 31, 2026. Any additional payments are subject to our agreement and cannot currently be estimated.

Legal proceedings

Putative Securities Class Action

On February 4, 2026, a putative class action complaint was filed in the United States District Court for the Southern District of New York against the Company, its Chief Executive Officer, Denise Scots-Knight, and its Chief Scientific Officer, John Lewicki (the “Defendants”). This action, captioned Dodge v. Mereo Biopharma Group PLC (No. 1:26-cv-988), alleges that the Defendants violated federal securities law by making false and misleading statements regarding the Company's business and operations. The Plaintiff seeks the payment of damages allegedly sustained by her and the putative class by reason of the allegations set forth in the complaint, plus interest, and legal and other costs and fees. On April 29, 2026, the court appointed a lead plaintiff and lead counsel. No responsive pleadings have been filed to date. The Company intends to vigorously defend against this action, but at this early stage, the Company can neither predict the ultimate outcome, nor estimate any range of possible losses.

From time to time, the Company may be a party to litigation or subject to claims incident to the ordinary course of business. Except for the abovementioned putative securities class action, the Company was not a party to any material litigation and did not have any material contingency reserves established for any liabilities as of March 31, 2026 and December 31, 2025.