In order to provide enhanced medication safety for inpatients, the medical mechanism which adopts the modified grouping proof protocol is proposed in this paper. By using the grouping proof protocol, the medical staffs could confirm the authentication and integrity of a group of Radio-Frequency Identification (RFID) tags which are embedded on inpatient bracelets and the containers of drugs. This mechanism is designed to be compatible with EPCglobal Class-1 Generation-2 standard which is the most popular specification of RFID tags. Due to the light-weight computational capacity of passive tags, only the pseudo-random number generator (PRNG) and cyclic redundancy code (CRC) are allowed to be used in the communication protocol. Furthermore, a practical scenario of using this proposed mechanism in hospital to examine the medication safety is also presented.