This double-blind, placebo-controlled randomized pilot clinical trial will test the hypothesis that granules of CDD-2105, a Chinese herbal medicine formula, will have efficacy in alleviating constipation and abdominal pain in individuals with IBS-C. Participants (n=78) will be randomly assigned to the treatment or placebo group in a 1:1 ratio, followed by 4 weeks of intervention and 4 weeks of follow-up.