Impact of a free medication policy on blood pressure among older patients with hypertension: an interrupted time series analysis

With the intensification of aging in China, limited medication access and financial burden hinder effective blood pressure management in older adults. In July 2021, Quzhou introduced a policy providing free antihypertensive medications to individuals aged ≥ 65 years. This study aimed to evaluate its impact on long-term blood pressure outcomes.

An interrupted time series analysis was performed using 28 quarters of longitudinal blood pressure data from 1,310 older patients with primary hypertension (aged ≥ 65 years) in Quzhou. A segmented regression model embedded with quarterly seasonal dummy variables was constructed to adjust for long-term physiological trends and seasonal blood pressure fluctuations. Autocorrelation was diagnosed by Durbin-Watson and Breusch-Godfrey tests, and counterfactual prediction was applied to quantify the net policy effect.

Prior to the policy, DBP showed a slow declining trend (-0.048 mmHg per quarter) while SBP exhibited a significant upward trend (0.275 mmHg per quarter). The policy produced no immediate level change but significantly altered long-term trajectories. Following implementation, the rate of DBP decline accelerated by an additional − 0.062 mmHg per quarter (P = 0.029), whereas SBP trend reversed from an increase to a decrease, resulting in a net change of -0.310 mmHg per quarter (P < 0.001). By the fourth quarter of 2024, actual SBP was 4.4 mmHg lower than the counterfactual scenario without the policy, and DBP was 0.8 mmHg lower. The cumulative policy effects over the entire follow-up period were 6.6 (95%CI: -1.2, 14.3) mmHg for DBP and 32.2 (95%CI: 13.6, 50.8) mmHg for SBP.

The free antihypertensive medication policy in Quzhou is not only a social welfare initiative but also an effective public health intervention with significant clinical benefits. It significantly altered the long-term trajectory of blood pressure among elderly patients by accelerating the decline in diastolic blood pressure and reversing the upward trend in systolic blood pressure.