Mechanisms of Alcohol Tolerance (R21/R33 Clinical Trial Optional) | PAR 21 250

Opportunity Information: Apply for PAR 21 250

The Mechanisms of Alcohol Tolerance (R21/R33 Clinical Trial Optional) opportunity (Funding Opportunity Number PAR-21-250) is an NIH discretionary grant in the health area (CFDA 93.273) that targets the biological and computational foundations of alcohol sensitivity and tolerance as they relate to the development of alcohol use disorder (AUD). The core purpose is to push the field toward clearer, testable explanations for why some individuals or systems become tolerant to alcohol and how that tolerance may accelerate risk for AUD. In practical terms, the announcement encourages projects that move beyond description and into mechanism, meaning applicants are expected to propose concrete, evidence-driven ideas about how tolerance is regulated and how it evolves over time.

The FOA highlights two main scientific aims. First, it seeks the development of hypotheses about cellular, molecular, or network-level mechanisms that control alcohol sensitivity and tolerance. This can include, for example, signaling pathways, receptor and ion channel adaptations, synaptic and circuit changes, gene expression and epigenetic regulation, glial and neuroimmune contributions, or broader neural network dynamics that shift with repeated alcohol exposure. Second, it invites the development of quantitative models capable of predicting tolerance development and the trajectory toward AUD. This modeling emphasis signals interest in approaches that can turn biological and behavioral data into predictive frameworks, such as computational neuroscience models, statistical or machine learning models, dynamical systems models, or multiscale models linking molecular changes to circuit function and behavior. The overarching theme is prediction plus mechanism: identifying what changes, how it changes, and whether those changes can forecast problematic escalation.

This is structured as a Phased Innovation award using the R21/R33 mechanism, which is designed to support early, high-impact work that can mature into a more expansive research program if initial milestones are met. The R21 phase is intended for secondary data analysis and/or pilot studies that de-risk the concept, refine measures, establish feasibility, and generate preliminary evidence. The R33 phase is where applicants scale up to fully test the hypotheses and models developed earlier, using stronger designs, larger datasets, or more comprehensive experimental and analytic work. A key feature is that moving from R21 to R33 is not automatic; NIAAA program staff will evaluate whether the R21 milestones were achieved and will decide on the transition based on those predefined benchmarks. Because of this, a competitive application typically needs clear, measurable R21 milestones that logically set up the R33, along with explicit go/no-go criteria.

Clinical trial participation is optional, meaning the FOA can support projects that do not involve clinical trials as well as those that do, depending on the question and approach. Applicants can therefore propose preclinical, translational, computational, or human-focused research, as long as the work aligns tightly with the goals of uncovering mechanisms of tolerance/sensitivity and building quantitative models related to tolerance and AUD progression. The inclusion of secondary data analysis in the early phase also makes the opportunity relevant to teams with access to existing datasets who can generate strong mechanistic hypotheses and model prototypes before investing in expanded experimental work.

Eligibility is broad and includes many types of organizations. Eligible applicants span state, county, city or township governments, special district governments, independent school districts, and public housing or Indian housing authorities, as well as public and state-controlled institutions of higher education, private institutions of higher education, nonprofits (with or without 501(c)(3) status), for-profit organizations (other than small businesses), and small businesses. It also explicitly welcomes a wide range of mission- and community-centered institutions and entities, including Alaska Native and Native Hawaiian Serving Institutions, AANAPISIs, Hispanic-serving Institutions, Historically Black Colleges and Universities, Tribal governments (federally recognized and other than federally recognized), Tribal colleges and universities (including TCCUs), faith-based or community-based organizations, U.S. territories or possessions, and non-U.S. (foreign) organizations, as well as regional organizations and eligible federal agencies. This breadth suggests the program is open to diverse research environments and encourages participation from institutions that serve historically underrepresented or geographically dispersed communities.

Administratively, the sponsoring agency is the National Institutes of Health, with the National Institute on Alcohol Abuse and Alcoholism (NIAAA) overseeing programmatic decisions such as the R21-to-R33 transition. The original closing date listed is 2024-09-07, and the FOA was created on 2021-06-22. The award ceiling and expected number of awards are not specified in the provided listing, which typically means applicants should consult the full FOA details and NIH budget guidance for the mechanism to understand allowable costs, project period structure, and any institute-specific limits or expectations.

Overall, this opportunity is aimed at projects that can credibly connect mechanistic biology and/or neural circuitry with rigorous quantitative modeling to explain and predict alcohol tolerance and AUD risk, using a staged plan where initial pilot or secondary analyses generate the evidence and milestones needed to justify a larger, hypothesis-testing expansion in the R33 phase.

• The National Institutes of Health in the health sector is offering a public funding opportunity titled "Mechanisms of Alcohol Tolerance (R21/R33 Clinical Trial Optional)" and is now available to receive applicants.
• Interested and eligible applicants and submit their applications by referencing the CFDA number(s): 93.273.
• This funding opportunity was created on 2021-06-22.
• Applicants must submit their applications by 2024-09-07. (Agency may still review applications by suitable applicants for the remaining/unused allocated funding in 2026.)
• Eligible applicants include: State governments, County governments, City or township governments, Special district governments, Independent school districts, Public and State controlled institutions of higher education, Native American tribal governments (Federally recognized), Public housing authorities/Indian housing authorities, Native American tribal organizations (other than Federally recognized tribal governments), Nonprofits having a 501 (c) (3) status with the IRS, other than institutions of higher education, Nonprofits that do not have a 501 (c) (3) status with the IRS, other than institutions of higher education, Private institutions of higher education, For-profit organizations other than small businesses, Small businesses, Others.

Apply for PAR 21 250

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