An implantable medical device (IMD) includes an adjustable capacitive voltage multiplier (CVM) that is responsive to diagnostic circuitry configured to provide control signals within a single stimulation current pulse for adjusting the voltage output applied to an electrode of the IMD's lead system. A control counter is coupled to the diagnostic circuitry for incrementing or decrementing an N-bit counter output signal operative to reconfigure a charge pump arrangement of the CVM so as to facilitate an adjusted voltage output.