In this double-blind, randomized clinical trial, 36 healthy male volunteers were randomly distributed into three groups (n = 12) that underwent a three-step treatment. For four consecutive days, we alternately administered a standardized dried extract of Equisetum arvense (EADE, 900 mg/day), placebo (corn starch, 900 mg/day), or hydrochlorothiazide (25 mg/day), separated by a 10-day washout period. Each volunteer served as his own control, and the groups' results were compared. We repeated the same evaluation after each stage of treatment to evaluate the safety of the drug. The diuretic effect of EADE was assessed by monitoring the volunteers' water balance over a 24 h period. The E. arvense extract produced a diuretic effect that was stronger than that of the negative control and was equivalent to that of hydrochlorothiazide without causing significant changes in the elimination of electrolytes. There was no significant increase in the urinary elimination of catabolites. Rare minor adverse events were reported. The clinical examinations and laboratory tests showed no changes before or after the experiment, suggesting that the drug is safe for acute use. Further research is needed to better clarify the mechanism of diuretic action and the other possible pharmacological actions of this phytomedicine.

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To assess the profile and causality of adverse events related to herbal medicines of widespread use in Brazil, we conducted an open, prospective, before-and-after clinical trial with patients at an outpatient clinic specialized in complementary and alternative medicine. Participants were submitted to laboratory tests prior to and after use of the medicines, as well as following a period of discontinuation in those experiencing adverse events. Occurrence of adverse events and their severity were verified in accordance with the WHO Toxicity Grading Scale for Determining the Severity of Adverse Events, and their causality established via the Naranjo algorithm. Forty-two subjects participated in the trial, of which 25 experienced grade 1 toxicity adverse events, mainly hyperamylasemia, and 14 continued to experience them following discontinuation, mainly hypomagnesemia. Mean/median values of laboratory tests performed in each phase were within specifications. Statistical analysis of these values in pre-treatment and treatment (n=42) and in treatment and post-treatment phases (n=22) showed statistical significance for activated partial thromboplastin time (p=0.020) in the first correlation. The Naranjo algorithm established a possible causal relationship between the use of herbal medicines and the adverse events reported. By signaling a low probability of occurrence, the algorithm indicates the safe use of these medicines under the experimental conditions employed.