Validation of New Type Radiopaque Marker in The Evaluation of Colonic Transit Time

The goal of this clinical trial is to learn if the local made colonic transit capsule can be use to diagnose slow transit constipation. The main questions it aims to answer are: * Does the local made colonic transit capsule correlate with the standard colonic capsule in the diagnosis of slow transit constipation? * Does the number of remained radiopaque marker similar between the two test after five days of ingestion? Researchers will compare the local made colonic capsule with the standard Sitzmark colonic capsule to see the correlation. Participants will: * Take both local made colonic capsule and Sitzmark colonic capsule at the same time. * Obtain abdominal x-ray 5 days after capsule ingestion. * Keep a diary of their symptoms and medication used during investigation.