The main purpose of the capsule is to prevent the burn of the medicine on the esophagus. What is not conventionally recognized is to protect the capsule from rupture in the stomach, but to reduce irritation to intestinal absorption. Because the general gelatin capsules (accounting for the absolute majority) will still rupture under the acidic conditions of the stomach. Capsules are generally considered to be classified as follows:

1) Hard capsules, soft capsules

2) Two-section capsule, one-piece capsule

3) Capsules with solid contents, capsules with liquid contents, capsules with semi-solid contents

4) Conventional capsules, microcapsules

5) Controlled-release capsules, ordinary capsules (capsules such as sustained-release, targeted, gastric-coated, enteric-coated, and gastric-floating capsules all belong to the controlled-release category)

Enteric-coated capsules exist, but they are different from conventional capsule shells. The capsule shells are made of special materials, which do not dissolve under the acidic conditions of the stomach and do not cause much deformation. They will only dissolve in the pH environment of the intestinal tract.

Sustained-release capsules do not rely on the sustained-release effect produced by the capsule shell, but by the particles in the capsule. It is imagined that the rupture of the capsule shell is almost instantaneous, and all the medicines in the capsule are released to the corresponding parts in an instant, which cannot slowly release the medicines therein. In fact, the principle of sustained-release capsules is similar to making the active ingredient granules into something like "tube sugar", which slowly melts and absorbs in the intestinal tract.