Background: Probiotics and antispasmodics have been tested extensively in the management of symptoms of irritable bowel syndrome (IBS), but they have rarely been evaluated in combination. The objective of this pilot study was to assess the efficacy of treatment with the probiotic formulation i3.1 (Lactobacillus plantarum CECT7484 and CECT7485 and Pediococcus acidilactici CECT7483), with or without the addition of the antispasmodic alverine/simethicone, in improving IBS-related quality of life (QoL) and reducing abdominal pain and diarrhea in patients with IBS. Methods: This was a randomized, placebo-controlled clinical trial with 3 parallel arms (probiotic, probiotic plus antispasmodic, and placebo). Patients with IBS (N = 55) were recruited at the Gastroenterology Department of the Juárez Hospital (México City). QoL was assessed with the IBS-QoL questionnaire, abdominal pain with a visual analog scale, and stool consistency with the Bristol scale. Results: The IBS-QoL rate of response (ITT analysis) was 50.0% for patients in the group with probiotic alone, 68.4% in the group with probiotic plus antispasmodic, and 16.7% in the group with placebo after 6 weeks of treatment (p = 0.005). Response to abdominal pain was reported by 38.9% of patients treated with probiotic, 57.9% with probiotic plus antispasmodic, and 16.7% with placebo (p = 0.035). Regarding stool consistency, a response to treatment was reported by 44.4% of patients treated with probiotic, 57.9% with probiotic plus antispasmodic, and 16.7% with placebo (p = 0.032). Conclusion: The results are consistent with previous studies on the use of the i3.1 probiotic formulation for the management of symptoms in IBS patients, and the addition of an antispasmodic improves its observed effects.