Does Black Seed Reduce Blood Pressure?
Mennat-Allah Abdin, Katelin Everitt, Kerina Gibb
Black seed is a flowering plant from southwest Asia and the Mediterannean where it is used commonly for diabetes, hypertension, asthma, COPD, inflammation, bacterial infections, and many more indications.1,2,3 In this project, we hope to determine the safety and efficacy of using black seed for hypertension. There are many proposed mechanisms for black seed with all of them claiming different parts of the plant and different chemicals as the active ingredient. The mechanism for its antihypertensive effects is not known. However, there is substantial evidence to indicate that it could work through a diuretic-like mechanism.1 Other proposed mechanisms for the antihypertensive effects include regulation of endothelial function and inhibition of calcium channels.1
A few studies and case reports have documented the potential risks of using black seed. The most common side effects reported with black seed are nausea, vomiting, constipation, gastric burning, contact dermatitis, and maculopapular eruptions.1 Renal dysfunction has also been seen when using black seed.1 Animal studies have shown that using black seed can lead to hepatotoxicity, although this has not been seen in humans.1 Black seed has potential interactions with anticoagulants, antiplatelets, antihypertensives, antidiabetics, CNS depressants, serotonergic drugs, and immunosuppressants.1 It should be avoided in patients with bleeding disorders, perioperatively, and in pregnancy due to its anticoagulant effects.1
We examined two studies to help determine the efficacy of black seed for hypertension. The first study was a systematic review and meta analysis of 11 randomized controlled trials studying black seed’s utility in hypertension. The studies’ durations varied from 4-12 weeks.4 After compiling the results from the 11 studies, they found that black seed lowers the SBP by 3.26 mmHg and the DBP by 2.80 mmHg when compared to placebo.4 They also found that the powder had greater effects on blood pressure than the oil.4 The study suffered from a high amount of heterogeneity among the different randomized controlled trials they included.
The second study was a randomized controlled trial comparing placebo to 100 mg and 200 mg of black seed.5 The study only included male patients with mild hypertension who were naive to therapy with antihypertensives, so it suffered from a lack of generalizability.5 After 8 weeks, they found that black seed lowers the SBP and the DBP by about 2 mmHg.5
Overall, we concluded that the evidence does show that black seed can lower blood pressure by about 2-3 mmHg, but the effect is so low that it has no real clinical significance.4,5 We would not recommend black seed to a patient for hypertension because of the lack of clinically significant efficacy and its side effects in addition to the risks poorly treated hypertension.