Abstract
Herbs have been used worldwide for many health conditions as an alternative treatment, including hypertension. Their use might affect the use of conventional medications, as well as blood-pressure control. This study aims to determine whether the potential associations between herb use and high blood pressure in hypertensive patients was mediated by medication adherence. A cross-sectional study was conducted using questionnaires and available medical databases at a primary care clinic of a tertiary hospital in Chiang Mai, Thailand. The data were collected from 450 patients with essential hypertension. Drug adherence was assessed by the Morisky Green Levine Medication Adherence Scale. The history of herbs used in the past three months was obtained. The goal of controlled blood pressure was defined in accordance with the Thai guidelines on the treatment of hypertension. Of the total 450 patients, 42% had high adherence. Nearly 18% reported herb use in the past three months. High medication adherence was strongly associated with blood-pressure control when adjusted for age, gender, education, the presence of comorbidities, and herb use (aOR 26.73; 95% CI 8.58-83.23; p < 0.001). The association between herb use and blood-pressure control did not achieve statistical significance (p = 0.143). However, the adjusted odds ratio of the association between herb use and blood-pressure control was diluted from 0.67 to 0.83 when adding the factor of medication adherence to the model. In conclusion, herb use was associated with poor medication adherence, which was in turn associated with poor blood-pressure control. Assessing this information contributes to appropriate exploration and counseling.