A desired effect is produced by therapeutically activating tissue at a first site within a patient's body and a corresponding undesired side effect is reduced by blocking activation of tissue or conduction of action potentials at a second site within the patient's body by applying high frequency stimulation and/or direct current pulses at or near the second site. Time-varying DC pulses may be used before or after a high frequency blocking signal. The high frequency stimulation may begin before and continue during the therapeutic activation. The high frequency stimulation may begin with a relatively low amplitude, and the amplitude may be gradually increased. The desired effect may be promotion of micturition or defecation and the undesired side effect may be sphincter contraction.