Study Design
The current study is a triple-blind, placebo-controlled, cross-over, 4-week clinical trial with a 4-week washout period. Details and procedures of the study were completely explained to patients through an interview, consent was obtained before the start of study treatment. This clinical trial was conducted in accordance with the ethical principles that have their origin in the Declaration of Helsinki, and that are consistent with Good Clinical Practice (GCP) and the applicable regulatory requirements. Moreover, the study is in compliance with the regulations of Iran and approved by an independent ethics committee of Mashhad University of Medical Sciences, Mashhad, Iran (ethics committee reference number and approval date: IR.MUMS.REC.1394.705, 2016-02-27). This clinical trial was registered at the Iranian Registry of Clinical Trials (www.irct.ir, IRCT registration number and date: IRCT20130418013058N8, 2018-04-22). In the first step, 51 hypertensive patients were allocated into celery and placebo groups (Figure 1). The patients received four capsules per day (2 capsules every 12 hours before meal) for 4-weeks as a supplement to their usual medication regimen. After a 4-week washout period, in the second step, the patients were crossed over into another medication group. Therefore, the patients who had received celery extract in the first step received placebo capsules after the cross-over, and those who had received placebo in the first step received celery extract capsules in the second step. The participants were not allowed to change their medication regimens or lifestyles during the study. Patient compliance with medication and trial process was assessed through weekly phone calls and at each visit to the physician.