The aim of this study was to place Forlax in its therapeutic class comparing its efficacy and its tolerance with Transipeg in the treatment of adult's chronic constipation. A total of 256 outpatients suffering from chronical idiopathic constipation (38 males and 218 females, mean age 51) have been included in a double blind multicentric study run on two parallel groups. Patients have been treated with 1 to 3 intakes daily, adapting themselves the posology to obtain the therapeutic result that would give them satisfaction. The length of the study was of 4 weeks with 3 consultations on D0, D14 and D28. Patients collected every day the frequency and consistency of their stools, the conditions of evacuation, the presence of digestive symptoms; each week the global improvement of the constipation on a visual analogical scale (VAS) and at the end of the period, their opinion on the global digestive state, the quality of life during the study and the taste of the medicine (VAS). The physician also was giving an efficacy score at the end of the study. Frequency and intensity of adverse events were low and identical in both groups. Forlax is significantly more effective than Transipeg: as much on the global improvement of the constipation expressed by the patient (p < 0.001), as on the evolution of the number of stools (p < 0.001). Efficacy has been noticed by the follow-up of the physician who gave a 76.1 score to Forlax against a 56.2 score to Transipeg (p < 0.001) and only with Forlax a stool per day was obtain after the first week of administration. Patients are more satisfied with Forlax which improve significantly their global digestive satisfactory index (p < 0.001) with favourable repercussion on their quality of life (p < 0.001). The taste of Forlax was very much appreciated by the patients (p < 0.001).