Purpose: Onopordon acanthium L. is known for its medicinal properties. Our recent study showed that its seed extract is a novel natura angiotensin-converting-enzyme inhibitor (ACEI). This study was carried out to investigate its possible antihypertensive effects in patients receiving losartan. Methods: This uncontrolled clinical trial was carried out among 20 patients (30-60y) with uncontrolled hypertension despite receiving 50 mg losartan (stage I & II) in two hospitals in Iran. After completing informed consent, patients were treated by 2 capsules [each 1g of Onopordon acanthium seed extract (OSE)] as add-on therapy, two times per day. Results: 18 patients completed the study (50.94 ±8.37y). Mean systolic blood pressure (SBP) at the baseline was 151.9 ± 13.74mmHg and at the end of the study, it was 134.6 ± 18.25 mmHg and mean diastolic blood pressure (DBP) was 97.41 ± 10.36 at the baseline and was 85.71 ± 7.481 after 8 weeks. OSE significantly reduced SBP and DBP at the end of 8 weeks (P=0.003, 95% CI: -19.7, -15.1; P=0.0006, 95% CI: -10.23, -13.15; respectively). No evidence of hepatic or renal toxicity was detected. Conclusion: Based on the results of this study OSE has antihypertensive property with no significant adverse effects. However, because of the low number of samples, this medication may be not safely administered. The results of this study could be the basis for further studies with larger sample size. IRCT registration number: IRCT2013020712391N.
Keywords: Angiotensin converting enzyme; Blood pressure; Hypertension; Onopordon acanthium L; Persian medicine.