The clinical trial has a randomized, double-blind and placebo-controlled design, in which the effect of a probiotic mix wants to be evaluated, with a treatment of 12 weeks, in the evolution of the symptoms of Irritable Bowel Syndrome.

The 12 weeks of the treatment are structured in four in-person visits: Visit 1 (initial; week 0), Visit 2 (halfway; week 4), Visit 3 (halfway; week 8) and Visit 4 (final; week 12).

Below, the four visits that compose the study and what to do in each one of them are described:

Visit 1 or initial (Week 0)

With the aim of recruiting patients, all patients diagnosed with irritable bowel who go to a consultation in the participant centres shall be informed of the study. If the patient shows interest, they shall be given detailed information about the study and the implications of their participation so that they can sign the informed consent if they wish so. Before signing, the patients shall have enough time to read and consider the detailed information and ask the investigator. The process of recruitment of patients shall continue until the sample size is reached.

Once the informed consent is signed, a doctor trained for the study shall make the initial interview in which the patient is tested to meet all the criterion for inclusion and none for exclusion (see clause 5.3.) and their clinical history.

The investigator shall proceed to assign to the patient the participant number on the study and, according to a previously elaborated randomization list, they shall be assigned the treatment that they shall receive during the study.

Once gotten to this point, the investigator shall value the severity and the symptoms of the Irritable Bowel Syndrome, by means of the IBS-SSS and IBS-QOL questionnaires (Annex I and II).

The patient shall be given the treatment with the assigned code, enough for the next programmed visit.

They shall be asked to turn in a stool sample and the nurse staff shall take a blood sample.

Visit 2 (Week 4) and visit 3 (Week 8)

In the halfway visits, in addition to value the symptoms of the disease with the scales detailed on the variable clause, the investigator shall register the adverse occurrences reported by the patient in a Case Report Form (CRF), as well as the concomitant treatments used.

Furthermore, the compliance rate of the treatment shall be calculated through the counting of the vials given back by the patient.

The patient shall be given new treatment, with the same code, enough until the next visit.

Visit 4 (Week 12)

In this visit the symptoms of the disease shall be valued with the two scales used in the study and the treatments that the patient has required during the 12 weeks following the end of the treatment under consideration.

Same as the first visit, they shall be asked to turn in a stool sample and they shall be taken a blood sample.

Inclusion Criteria:

• Aged between 18-65 years old.
• Informed consent signed by the patient.
• Patients with Irritable Bowel Syndrome diagnosed by Roma IV criteria

Exclusion Criteria:

• Patients who took antibiotics until two weeks prior to study.
• Patients who have taken other probiotics two months prior.
• Patients with other intestinal inflammatory diseases.
• Pregnant, breastfeeding or patients who do not compromise to use an efficient contraceptive method during the development of the study.