This paper introduces a novel self-triplexing implantable antenna designed to operate in head implants. It works at three distinct frequency bands: 403 MHz on Port 1, 915 MHz on Port 2, and 1410 MHz on Port 3. The antenna design incorporates a high-permittivity laminate and triangular meandered resonators, which extend the current path and enable significant miniaturization. The resulting antenna occupies a volume of only 8 mm × 12.5 mm × 0.3 mm (30 mm3). An ultra-thin substrate of 0.3 mm is utilized to reduce mutual coupling between the ports, achieving values below -24.3 dB. By activating each port of the antenna with 1W power, the 10-g specific absorption rate (SAR) values are recorded at 45.9, 42.4, and 41.2 W/kg for the frequencies 403, 915, and 1410 MHz, respectively. The antenna exhibits peak gains of -35.7, -31.3, and -28.6 dBi at the respective frequencies. Comprehensive link budget and SAR analyses demonstrate the antenna's potential for head implant applications. The validation of the fabricated prototype is conducted through measurements inside minced pork meat. Additionally, two software-defined radios are used to practically validate the simultaneous transmit and receive capabilities. To the authors' knowledge, this is the first self-triplexing implantable antenna, a promising choice for next-generation implantable devices.