The plant species Ageratina pichinchensis has been used, for many years, in Mexican traditional medicine for the treatment of superficial mycosis. Aim of the study: This study compared the therapeutic effectiveness and tolerability of two concentrations of the standardized extract from Ageratina pichinchensis (12.6 and 16.8%) on patients with clinical and mycological diagnosis of mild and moderate onychomycosis. Materials and methods: Two identical phytopharmaceuticals (containing the standardized extract from Ageratina pichinchensis) in nail lacquer solution for topical administration were evaluated in a double-blind clinical trial. Treatments were administered for 6 months to patients distributed in two groups. Results and discussion: Of 122 patients who agreed to participate in the study, 103 (84.4%) concluded the treatment. The therapeutic effectiveness exhibited by the 12.6% Ageratina pichinchensis extract was 67.2%, while that of the 16.8% Ageratina pichinchensis extract was 79.1%. Regarding clinical evolution, analysis of results at the end of treatment evidenced that the 16.8% concentration possesses higher therapeutic effectiveness with a significant statistical difference (p=0.010). No treatment produced side effects. Conclusion: Both concentrations of phytopharmaceuticals possess high rates of effectiveness on patients with mild and moderate onychomycosis, and the formulation with a 16.8% concentration possesses higher effectiveness.