Embodiments disclosed herein relate to methods, devices, and computer systems thereof for reducing stomach volume in a subject. In certain embodiments, a subject receives a stomach-volume-reducing device that optionally includes at least one reservoir configured to release at least one appetite suppressant. In an embodiment, the stomach-volume-reducing device is responsive to one or more environmental conditions of the subject, for example, pH or chemical chemicals in the stomach of the subject. In an embodiment, the stomach-volume-reducing device controls hunger in the subject.