Evaluation of the Bronchodilator Effect of Guaco Syrup: a Randomized, Double-blind, Crossover Clinical Trial

Guaco is an herb used to treat respiratory disorders. It is included in the list of drugs offered by the Brazilian health system, however its efficacy has never been assessed by clinical trials. A randomized, double-blind, crossover clinical trial was conducted to evaluate the bronchodilator activity of guaco syrup (Mikania glomerata Spreng., Asteraceae) compared with salbutamol and placebo in volunteers presenting with bronchoconstriction. Fifteen volunteers were analyzed. Mean changes in expiratory values of each group, as well as the percentage increase to baseline and to the predicted value were compared. Guaco was statistically different from salbutamol (p < 0.001 for all three outcomes), and it was not different from placebo (p values of 0.824, 0.295, and 0.760). No adverse events were reported during trial. A bronchodilator effect resulting from guaco syrup was not observed in this trial. Other clinical trials should be conducted to explore alternative mechanisms of actions of guaco and, hence, support or reject the use of this herb in the treatment of respiratory disorders. Trial registration: RBR-4n26tf