Which herb has documented interactions with antihypertensives, including cardiac glycosides, beta blockers, and calcium channel blockers?

• A. Selenicereus grandiflorus
• B. Usnea barbata
• C. Tanacetum vulgare
• D. Tribulus terrestris

Answer: (D)

Understanding how certain herbs can amplify the blood-pressure–lowering effects of antihypertensive medications helps explain why this herb stands out. Tribulus terrestris has documented interactions with antihypertensives across several drug classes, including cardiac glycosides, beta blockers, and calcium channel blockers. Its active constituents can influence vascular tone and electrolyte balance, which can potentiate the hypotensive and heart-rate–lowering actions of these medications. In practice, this means a higher risk of excessive blood pressure drop, bradycardia, or rhythm disturbances when Tribulus is used with digoxin-like drugs, beta blockers, or calcium channel blockers. Because of this broad interaction potential, it is the herb most consistently associated with these antihypertensive interactions.

The other options don’t have as strong or as broad a documentation of interactions with these specific antihypertensive classes.