Why the blood pressure pill amlodipine can make ankles swell
Amlodipine was the fifth most prescribed medicine in the United States in 2023, with more than 68 million prescriptions. It lowers blood pressure by relaxing arteries, but it opens the small inflow vessels more than the outflow ones, and that mismatch pushes fluid into tissues, which is why swollen ankles are its best-known side effect.
Chemically it is a dihydropyridine, a long-lasting kind of calcium channel blocker, marketed as Norvasc among other names. It was patented in 1982, approved for medical use in 1990, and now appears on the World Health Organization's list of essential medicines as a cheap generic. Doctors use it for high blood pressure, coronary artery disease and a spasm-driven form of chest pain called variant angina, and it is a first choice for Raynaud's phenomenon.
The swelling has a neat mechanical explanation. Amlodipine widens arterioles and precapillary vessels more than the venules downstream. Extra blood flows in but meets relatively narrow exits, and the pressure forces plasma out into surrounding tissue. At the highest common dose, about 10.8 percent of people develop this peripheral oedema, against 0.6 percent on placebo, and women are three times more likely to be affected than men. Pairing it with an ACE inhibitor or an angiotensin receptor blocker can prevent the problem, which is one reason so many combination pills exist.
Other effects that rise with dose include palpitations, flushing and dizziness. Gum overgrowth is relatively common, especially where dental plaque builds up. The drug is also associated with a form of glaucoma. Its safety in pregnancy has not been established, and people with liver problems clear it more slowly.
Whether it protects against stroke better than rival drugs is still debated. Two meta-analyses saw no real gap in stroke prevention among the main drug classes, diuretics and ACE inhibitors included, while one 2015 analysis suggested calcium channel blockers came out ahead. Some evidence also points to greater stroke protection than beta blockers.
Source: Amlodipine
