Cotton Thistle Extract Lowers Blood Pressure in Patients Treated for Primary Hypertension

Hypertension increases the risk of stroke, myocardial infarction, vascular disease, and chronic kidney disease. Treatments for hypertension include drugs (angiotensin-converting-enzyme inhibitors, beta-blockers, diuretics, calcium channel blockers, alpha-blockers, and peripheral vasodilators) and improvements in lifestyle factors (losing weight, quitting smoking, reducing sodium intake, exercising regularly, and limiting alcohol intake). Among the specific drugs used to treat hypertension is losartan, an angiotensin receptor blocker. Cotton thistle (Onopordum acanthium, Asteraceae) seed extract (OSE) is among the herbal therapies used to lower blood pressure. These authors conducted an open-label, nonrandomized, uncontrolled clinical trial to investigate the possible antihypertensive effects of OSE in patients with stage I-II hypertension who are being treated with losartan.

Dried cotton thistle seeds purchased from the Grand Bazaar market in Tehran, Iran, were used to prepare the extract in the laboratory of traditional pharmacy at the Faculty of Traditional Medicine at Tehran University of Medical Sciences. Each capsule contained 1 gram of freeze-dried powder, which equaled 11 grams of dried seeds.

The authors conducted an evaluation in mice to measure the toxic dose of the OSE extract by injecting them with various doses of OSE. Referring to the results, the authors write that OSE was classified as “practically nonpoisonous.”

The 20 patients in the clinical trial had stage I-II hypertension according to the criteria outlined in the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Patients had been taking 50 mg of losartan daily for at least six weeks, and their blood pressure remained higher than 140/90 mmHg. They were aged 30 to 60 years and had been selected from Imam Khomeini and Amir-Alam hospitals of Tehran University of Medical Sciences. Baseline information included demographic data, medical history, and any other medications used.

Each patient took two OSE capsules two times daily for eight weeks. Blood pressure was monitored every other week. Those patients whose blood pressure increased more than 15 mmHg (one patient after two days and one patient after three days from baseline) were dropped from the study. Metabolic parameters (lipid profile, liver function tests, blood urea nitrogen, creatinine, and fasting blood sugar) were measured at baseline and at the end of the study.

Significant decreases in systolic blood pressure (SBP, P=0.025) and diastolic blood pressure (DBP, P=0.034) was observed after 45 days. After eight weeks, SBP decreased by 17.3 mmHg (P=0.003), and DBP decreased by 11.7 mmHg (P=0.0006).

No signs of hepatic or renal toxicity were observed. A tendency toward improvement was seen in glucose, the lipid profile, and blood urea nitrogen. Sodium and creatinine levels did not change. Two patients reported mild dyspnea after two weeks. During the first month of treatment, two patients complained of dizziness and a feeling of heaviness in the head, which later subsided.

Citing an earlier study, the authors attribute the hypotensive effects of OSE to its various components such as sesquiterpenes and flavonoids.1 The same study reported that OSE has a greater hypotensive effect than 50 other herbal agents that have been evaluated.

The authors conclude that OSE supplementation for eight weeks significantly decreased systolic and diastolic blood pressures in patients with stage I-II primary essential hypertension who were being treated with losartan. The authors caution that because of the small sample size used in the study, OSE may not be safely recommended until the results of additional placebo-controlled clinical trials confirm the findings of this study. The authors were limited by a small sample size because of the difficulty in recruiting patients with hypertension who were not using more than one drug to control their blood pressure. The exclusion of two patients presented an obstacle in obtaining results with a higher statistical power.

The authors report no conflicts of interest.


1Sharifi N, Souri E, Ziai SA, Amin G, Amini M, Amanlou M. Isolation, identification and molecular docking studies of a newly isolated compound, from Onopordon acanthium: a novel angiotensin-converting enzyme (ACE) inhibitor. J Ethnopharmacol. July 2013;148(3):934-939. doi: 10.1016/j.jep.2013.05.046.

Ghods R, Gharouni M, Amanlou M, Sharifi N, Ghobadi A, Amin G. Effect of Onopordon acanthium L. as add on antihypertensive therapy in patients with primary hypertension taking losartan: a pilot study. Adv Pharm Bull. March 2018;8(1):69-75. doi: 10.15171/apb.2018.009.