An in vivo RFID chip implanted in a patient's body, comprising an integrated antenna formed on the chip, and a CMOS-compatible circuitry adapted for biosensing and transmitting information out of the patient's body. In preferred embodiments, the CMOS-compatible circuitry is adapted to sense a chemical and/or physical quantity from a local environment in the patient's body and to control drug release from the drug reservoirs based on the quantity sensed.