Abstract: A controlled release capsule comprises a male plug (2) formed of a water swellable hydrogel which is engaged within a neck portion (4) of a female body (6). The capsule contains a pharmaceutically active material. In contact with an aqueous medium, such as in the gastrointestinal tract, the hydrogel plug swells and becomes disengaged from the body, thereby releasing the active material. In order to facilitate insertion of the male plug into the neck of the body, the body has a flared mouth portion (14) which is wider than the neck. The neck itself may be wider or narrower than the remainder of the body. A water-soluble cap (8) has detentes (18) which clip over the flared mouth portion so as to lock the cap thereto.