Organization	6 Months Ended
Jun. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Description of Business Prothena Corporation plc (“Prothena” or the “Company”) is a late-stage clinical biotechnology company with expertise in protein dysregulation and a pipeline of investigational therapeutics with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases. Fueled by its deep scientific expertise built over decades of research, the Company is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. The Company’s wholly-owned programs include a portfolio of programs for the potential treatment of Alzheimer’s disease including PRX012, which targets amyloid beta (Aβ) and PRX123, a novel dual Aβ-tau vaccine. The Company’s partnered programs include prasinezumab for the potential treatment of Parkinson’s disease and other related synucleinopathies that targets alpha-synuclein in collaboration with Roche. In addition, we have partnered BMS-986446 (formerly PRX005) for the potential treatment of Alzheimer’s disease that targets tau and PRX019 for the potential treatment of neurodegenerative diseases with an undisclosed target in two separate license agreements with Bristol Myers Squibb (“BMS”). The Company is also entitled to certain potential milestone payments pursuant to the Company’s share purchase agreement with Novo Nordisk pertaining to the Company’s ATTR amyloidosis business (inclusive of coramitug, formerly PRX004). The Company was formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market. Liquidity and Business Risks As of June 30, 2025, the Company had an accumulated deficit of $1.3 billion and cash and cash equivalents of $371.4 million. Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at June 30, 2025, are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and/or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. Additionally, in order to develop and obtain regulatory approval for our potential products the Company will need to raise substantial additional capital. The Company expects to continue to finance future capital needs that exceed its existing cash and cash equivalents from payments pursuant to its agreements with Roche, BMS, and Novo Nordisk, and, to the extent necessary, other collaborative agreements with corporate partners, or other arrangements, and through proceeds from public or private equity or debt financings, and loans including pursuant to the Amended Distribution Agreement (See Note 8, “Shareholders’ Equity” to the Condensed Consolidated Financial Statements for more information). The Company cannot assume that such additional financings will be available on acceptable terms, if at all, and such financings may only be available on terms dilutive to its shareholders.

Prothena Corporation plc (“Prothena” or the “Company”) is a late-stage clinical biotechnology company with expertise in protein dysregulation and a pipeline of investigational therapeutics with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases.

Fueled by its deep scientific expertise built over decades of research, the Company is advancing a pipeline of therapeutic candidates for a number of indications and novel targets for which its ability to integrate scientific insights around neurological dysfunction and the biology of misfolded proteins can be leveraged. The Company’s wholly-owned programs include a portfolio of programs for the potential treatment of Alzheimer’s disease including PRX012, which targets amyloid beta (Aβ) and PRX123, a novel dual Aβ-tau vaccine. The Company’s partnered programs include prasinezumab for the potential treatment of Parkinson’s disease and other related synucleinopathies that targets alpha-synuclein in collaboration with Roche. In addition, we have partnered BMS-986446 (formerly PRX005) for the potential treatment of Alzheimer’s disease that targets tau and PRX019 for the potential treatment of neurodegenerative diseases with an undisclosed target in two separate license agreements with Bristol Myers Squibb (“BMS”). The Company is also entitled to certain potential milestone payments pursuant to the Company’s share purchase agreement with Novo Nordisk pertaining to the Company’s ATTR amyloidosis business (inclusive of coramitug, formerly PRX004).

The Company was formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market.

Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at June 30, 2025, are sufficient to meet its obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development programs significantly above current long-term plans or enters into potential licenses and/or other acquisitions of complementary technologies, products or companies, the Company may need additional capital. Additionally, in order to develop and obtain regulatory approval for our potential products the Company will need to raise substantial additional capital. The Company expects to continue to finance future capital needs that exceed its existing cash and cash equivalents from payments pursuant to its agreements with Roche, BMS, and Novo Nordisk, and, to the extent necessary, other collaborative agreements with corporate partners, or other arrangements, and through proceeds from public or private equity or debt financings, and loans including pursuant to the Amended Distribution Agreement (See Note 8, “Shareholders’ Equity” to the Condensed Consolidated Financial Statements for more information). The Company cannot assume that such additional financings will be available on acceptable terms, if at all, and such financings may only be available on terms dilutive to its shareholders.