The goal of this clinical trial is to determine efficacy of FMT via rectal enema and encapsulated FMT in patients with IBS in Thailand. The main question it aims to answer is: • Does FMT provide better efficacy than placebo in IBS patients? Participants will be randomized into 3 groups: * In placebo group, patients will receive placebo capsules and placebo via enema. * In enema group, patients will receive placebo capsules and FMT via rectal enema. * In capsule group, patients will receive FMT capsules and placebo via rectal enema. Researchers will compare FMT and placebo group to see if using FMT provides better efficacy for IBS patients than placebo. Moreover, researchers will compare efficacy of FMT capsules and FMT via rectal enema in IBS patients.