Trends in female first authorship in addiction research: evidence from Spanish institutional affiliations in Q1 journals.

Gender disparities in scientific authorship remain a relevant issue in addiction research. This study aimed to examine temporal trends and regional differences in female first authorship among researchers affiliated with Spanish institutions publishing in high-impact journals. A bibliometric approach was applied to Q1 journals primarily focused on addiction research, with publications retrieved from inception to 31 December 2025. A total of 687 publications with first authors affiliated with Spanish institutions were identified, of which 48.6% had female first authors. Female first authorship increased substantially over time, from 35.3% in the period 1986-1995 to 54.7% in 2016-2025. Regression analysis confirmed a significant positive temporal trend (odds ratio = 1.036, 95% CI: 1.018-1.053, p < .001). Female first authorship in addiction research in Spain has increased significantly over time. Continued efforts are needed to promote equity and address structural barriers in scientific research, as the observed patterns may reflect the influence of multiple unmeasured factors.