HTR4 and Chronic constipation: Almost 50% of patients with chronic constipation are dissatisfied with the treatment of these drugs.[12] A clinical trial in which daily administration of 1 to 2 mg of procapride (agonist of serotonin receptor 4) was reported to restore BMS to normal in 37.9% of patients with severe chronic constipation.[13] However, the adverse cardiac effects caused by some prokinetic agents cannot be ignored.[14]