The aim of this clinical trial was to investigate the effects of Evelor, a micronized formulation of resveratrol (RESV; 3,5,4'-trihydroxy-trans-stilbene), in patients with primary hypertension. RESV is a stilbenoid and phytoalexin produced by several plants in response to injury or attack by pathogens, such as bacteria and fungi. Patients included in the clinical trial were split into the following two groups, based on the severity of their disease: Group A (n=46), stage I hypertension [systolic blood pressure (SBP), 140‑159 mmHg; diastolic blood pressure (DBP), 90‑99 mmHg] and Group B (n=51), stage II hypertension (SBP, 160‑179 mmHg; DBP, 100‑109 mmHg). Each group was divided into two subgroups: A1 and B1, patients treated with standard antihypertensive therapy (A1, 10 mg Dapril; B1, 20 mg Dapril), and A2 and B2, patients treated with antihypertensive therapy (Dapril) plus Evelor. The present study aimed to determine the effects of Evelor, in addition to the standard hypertension treatment, and its effect on the hepatic enzymes serum glutamate-pyruvate transaminase (SGPT) and gamma‑glutamyl transferase (gamma‑GT). Following the trial, which lasted two years (October 2010 to October 2012), the mean blood pressure of both groups lay within the normal range, indicating that blood pressure was efficiently controlled. The results of the present study demonstrate that the addition of RESV to standard antihypertensive therapy is sufficient to reduce blood pressure to normal levels, without the need for additional antihypertensive drugs. In addition, statistical analysis of the results identified a significant reduction in plasma concentration levels of SGPT (P<0.001) and gamma‑GT (P<0.001) with the addition of RESV, indicating that RESV prevents liver damage.