250 mg of celery stem extract — barely a thumbnail of powder — dropped diastolic pressure 15.2 mmHg in one trial. The mechanism isn’t fluid loss. It’s vascular smooth muscle relaxation.
Celery’s active compounds, called phthalides, lower blood pressure partly by relaxing the smooth muscle lining blood vessel walls — a mechanism distinct from how most diuretics work. That difference matters because most standard antihypertensive approaches reduce blood volume pressing against vessel walls, while phthalides appear to act on the walls themselves. A clinical trial using 250 mg of celery stem extract recorded a 9.59 mmHg systolic reduction and a 15.2 mmHg diastolic reduction — numbers that belong in a pharmacology discussion, not a crudité tray.
It’s a striking result from a plant most people reach for as a garnish.
What Phthalides Do Inside Blood Vessel Walls
Blood vessel walls contain a continuous layer of smooth muscle. When that muscle stays contracted, the channel narrows and pressure rises. Phthalides — specifically hydrophobic compounds like 3-n-butylphthalide and sedanolide — appear to interfere with calcium channel activity in that muscle tissue. Calcium channel interference in smooth muscle cells is the same basic lever that an entire class of pharmaceutical antihypertensives targets. Less calcium signaling means less contraction, wider vessels, lower resistance.
This mechanism operates alongside, not instead of, celery’s diuretic activity. The research describes celery as having vasodilatory, diuretic, and calcium channel-blocking properties simultaneously.
What Multiple Clinical Trials Actually Measured
The 250 mg trial result is real, but it sits inside a broader body of evidence. A randomized, triple-blind, placebo-controlled crossover trial found systolic pressure dropped from 141.2 to 130.0 mmHg and diastolic from 92.2 to 84.2 mmHg in the celery group. A separate 4-week study recorded daytime systolic falling 12.12 mmHg and daytime diastolic falling 8.89 mmHg. The 2025 meta-analysis — 10 RCTs, 511 participants — returned a standardized mean difference of -1.0 for systolic pressure and -0.93 for diastolic, both statistically significant. Celery seed preparations and doses above 1,000 mg/day showed the strongest signal across those trials.
Frequently Asked Questions
What are phthalides in celery?
Phthalides are hydrophobic bioactive compounds found in celery, including 3-n-butylphthalide and sedanolide, that appear to relax vascular smooth muscle and contribute to blood pressure reduction.
Does celery lower blood pressure by acting as a diuretic?
Celery has both vasodilatory and diuretic properties. The research does not support framing it as one or the other exclusively — both mechanisms appear active.
How much celery extract was used in clinical trials?
Trials have used 250 mg of stem extract, 250–300 mg/day ranges, and doses exceeding 1,000 mg/day, with the 2025 meta-analysis finding stronger effects at the higher end.
Is there strong clinical evidence, or just animal studies?
Multiple human clinical trials exist, and a 2025 meta-analysis of 10 randomized controlled trials with 511 participants confirmed statistically significant blood pressure reductions.