Antihypertensive Mechanisms of Minocycline in Resistant Hypertension

One hundred twenty patients with treatment-resistant hypertension will be enrolled. A total of 34 patients (17 from each treatment arm), who are participants in the main study, will also be enrolled in a substudy that includes neuroimaging. The study will last 3 months, and will include 3 visit time points (screening, randomization visit, 3-month follow-up visit). Participants will be randomly assigned, in a 1:1 allocation, to minocycline 100 mg twice per day, or matching placebo, each provided by the study, and investigators will be blinded to treatment assignment. At the baseline and 3-month follow-up visit, subjects will undergo: * A comprehensive medical history and examination, including assessment of antihypertensive treatment history * A series of behavioral activity questionnaires * Blood tests (plasma renin activity, aldosterone, catecholamines, serum creatinine, lipid panel, hemoglobin a1c, as well as various biomarkers of immune and inflammatory activity, and gut leakiness markers) * Urine/saliva tests for antihypertensive adherence * Gut microbiota profiling via whole metagenomic sequencing of stool samples * Blood pressure (BP) measurement, including unattended office BP and 24-hour ambulatory BP Subjects enrolled in the neuroimaging substudy will also have PET/MR imaging performed at each visit. Neuroimaging activities will take place at Emory University in Atlanta, GA. At the final visit (3-month follow-up), participants will also have blood tests to measure study drug concentration, as a measure of adherence to the assigned treatment.