Acute caffeine ingestion and exercise performance in women: a systematic review and meta-analysis of menstrual-cycle phase and hormonal contraceptive status.

Background: Acute caffeine ingestion is widely used to enhance exercise performance, but most evidence comes from male or mixed-sex cohorts. Whether menstrual-cycle phase or hormonal contraceptive status modifies caffeine's ergogenic effect in women remains unclear. Methods: Six databases were searched for randomized controlled trials examining acute caffeine ingestion and objective exercise performance outcomes in women. Methodological quality and risk of bias were assessed using a modified PEDro scale and RoB 2. Three-level meta-analyses accounted for dependent effect sizes within studies. The primary moderator was reproductive-hormonal status, classified as early follicular, late follicular/peri-ovulatory, luteal/mid-luteal, or hormonal contraceptive/oral contraceptive use. Exploratory analyses examined dose, exercise type, phase verification, timing, and habitual caffeine intake. Results: Twenty studies contributed 144 primary effect sizes. Acute caffeine ingestion improved exercise performance in women overall (Hedges' g = 0.37, 95% CI 0.24 to 0.50), with moderate heterogeneity and a prediction interval crossing the null. Positive estimates were observed across all reproductive-hormonal strata, but there was no clear evidence of between-stratum moderation. The overall effect was robust to outlier exclusion and alternative correlation assumptions. Exploratory analyses suggested that exercise-task phenotype and phase-verification method may partly explain variability in observed effects, whereas dose, timing, and habitual caffeine intake did not support phase-specific prescriptions. Risk-of-bias concerns, sparse subgroup data, and low-to-very-low GRADE certainty limited individualized inference. Conclusions: Acute caffeine ingestion produces a small average ergogenic effect in women, but exploratory findings suggest that its expression may vary by exercise task within different reproductive-hormonal contexts. Current evidence therefore supports a context-sensitive interpretation rather than rigid menstrual-phase- or contraceptive-specific prescriptions. However, given the low-to-very-low certainty of evidence, these findings should be interpreted cautiously and considered hypothesis-generating. Inconsistent phase verification remains a key methodological limitation that may obscure biologically meaningful patterns. Future female-specific trials should combine rigorous hormonal verification, detailed contraceptive profiling, prespecified exercise phenotypes, and mechanistic assessment to refine individualized caffeine guidance.. Systematic review registration: OSF https://osf.io/5y69g/, identifier 5y69g.