<qa>  What is the estimated prevalence of Functional constipation in Hong Kong?Functional constipation FC is common with 14.3 estimated prevalence in Hong Kong, but treatment for this condition in conventional medicine is suboptimal. Complementary and alternative medicines, especially Chinese herbal medicine CHM are used frequently by patients with FC, but there is little research evidence about these commonly used CHM. The purpose of the study is evaluate the efficacy and safety of CHM, as well as determining the optimal dosage. 