A multicenter, randomized, triple blind and controlled trial was designed to determine whether the combination with thioctic acid (TA), an antioxidant agent, can reduce the intolerance rate to Benznidazol (BZ) in patients infected with Trypanosoma cruzi. Four regimens were assigned randomly for 3 age intervals, administrating placebo or TA orally at daily doses of 50 to 100 mg in association with BZ at a dose of 5 mg/k/day for 30 days. In some, medication was given during a run-in period. Safety controls were carried out on days 10, 20, 37 and 52 days after therapy initiation. A total of 249 patients between 15 and 44 years old were enrolled. At the end of the trial, 70.3% of the patients had completed the treatment, while 17.7% required its suspension due to BZ related adverse reactions. The proportion of individuals affected with at least one side effect ranged from 54.8% to 58%; however, none were serious. Reported side effects included: cutaneous maculopapular rush (28%), pruritus (13.6%), headache (8%), epigastralgia (6.2%), fever (6.2%), fatigue (4.3%), nausea (4%), myalgias (4.3%), others (21.5%). The incidence of these reactions did not differ significantly among the 4 therapeutic regimens, nor even among the age intervals considered. It can be concluded that the association with TA did not prevent the occurrence of adverse reactions related to BZ administration. However, a single month cycle of this parasiticide permitted a high compliance rate to therapy among infected outpatients.