This will be a randomized, double-blinded, three-period crossover study of platelet activation and aggregation in 30 non-smoking healthy volunteers comparing chlorthalidone (CTD), hydrochlorothiazide (HCTZ), and aspirin (ASA; active control). The study hypothesis is that CTD has different effects on platelet activation and aggregation than HCTZ.

Inclusion Criteria:

• Men or women age 19 or older
• Not currently taking any routinely scheduled prescription or over the counter medications or herbal supplements
• No use of aspirin, clopidogrel, prasugrel, ticagrelor, cilostazol, dipyridamole, NSAID medications, or herbal supplements within the previous 7 days and able to refrain from use during the study period
• Systolic blood pressure > 110 mmHg and diastolic blood pressure > 60 mmHg
• Non-smoker

Exclusion Criteria:

• Previous adverse reaction or allergy to HCTZ, CTD, or ASA
• Severe sulfonamide hypersensitivity (anaphylaxis or Stevens-Johnson syndrome)
• Diagnosis of any chronic disease or condition
• History of gout or hyperuricemia
• History of pancreatitis
• History of systemic lupus erythematosus (SLE)
• History of hypokalemia requiring treatment
• Pregnant or planning to become pregnant during the study period
• Breastfeeding
• History of hypotension
• History of gastrointestinal bleeding