According to earlier research, antihypertensive medications (AHMs) that affect the renin-angiotensin system may slow the development of moderate cognitive impairment to dementia. There is a literature gap on causal relationships between AHMs use and Alzheimer's disease and related dementia (ADRD) risk, as well as related age, sex, and racial/ethnic disparities. This study aimed to employ double/debiased machine learning (DML) to clarify this relationship. Data from the Medicare Current Beneficiary Survey (MCBS) spanning from 2017 to 2019 was utilized in this study. ICD code, anti-dementia drugs use, and self-reported survey were used to identify ADRD patients. All FDA-approved AHMs were included in this study. Based on the newly released NIA Health Disparities Research Framework, a total of 47 covariates were used in our study. DML was employed to explore the causal relationship. Survey sampling weights were applied in this study to generate national estimates. A total of 87,112,516 were included in this study, among which 75.67% used AHMs and 11.34% were diagnosed with ADRD. Our results showed that taking AHMs could help decrease risks of ADRD by 1.7% (effect: 0.983, p < 0.001). Taking AHMs has no significant overall effect on individuals aged 65 to 74 but could help reduce ADRD risks for those aged over 75 (p < 0.001). AHMs use is effective in reducing ADRD risks for both males (p = 0.002) and females (p < 0.001). Notably, taking AHMs could help decrease ADRD risks for all races/ethnicities (p < 0.05) except for Hispanics (p = 0.772).This study illuminated the casual relationship of AHMs use in decreasing ADRD risks, as well as related age and racial/ethnic disparities. Our findings suggest that AHMs may be an effective antidementia therapy for ADRD patients with hypertension in routine care, but notable disparities need to be addressed.