Social anxiety is one of the most common disorders found in the population attending the first level of health care. Galphimia glauca has been used for many years in Mexican traditional medicine to treat "nervous disorders". A standardized extract of this species has been evaluated in clinical studies that have proven its efficacy and safety in patients with generalized anxiety disorder. In this work, a double-blind clinical trial was carried out, using sertraline as a control. Patients from both sexes (18 to 35 years old) with moderate or severe social anxiety were included. Experimental group was treated daily (orally), for 10 weeks, with an extract from G. glauca containing 0.374 mg/dose of Galphimine-B (G-B, active compound). Patients in the control group were given sertraline (50 mg) in the same conditions. All patients were evaluated every two weeks. Another assessment was done one month after the end of the administration period. A total of 34 patients was included, 17 in each group. Women were predominant, and the mean age was 25 ± 4.7 years. In patients who received the G. glauca standardized extract, a significant reduction in anxiety was observed, with a value (in the Brief Social Phobia Scale) of 41.1±10.3 points at the start and 11.2±5.6 points at the end of treatment, while patients treated with sertraline had a value of 37.7±7.3 points at the beginning and 11.1±5.2 points at the end. No significant difference was observed between the treated groups. In a similar way, the health scale showed a gradual and continuous improvement in each of the five evaluations. In conclusion, the 10-week oral administration of G. glauca standardized extract showed efficacy and safety in patients with social anxiety disorder, without showing a significant difference from patients treated with sertraline.