in the field of treatment of erectile dysfunction there is disclosed a novel therapy in which the actions of an agent or agents , produce a combination of effects to induce effective erection while reducing or entirely avoiding pain . the method taught combines a first action of an agent which is to antagonize a drug - induced pain stimulus within nociceptive nerves of penile tissue with a second action of either the same agent or of a second agent , which enhances , synergistically , smooth muscle relaxation . the synergism allows for at least an equivalent effect of smooth muscle relaxation to be obtained at significantly lower doses of a smooth muscle relaxing agent such as pge1 which in standard therapy is also in 40 - 45 % of cases pain - inducing at doses which achieve effective erection . thus in an anatomical site where nociceptive tissue is in close proximity to one or more effector systems , the method enhances the effector system while reducing nociception in the nociceptive tissue which nociception would be caused by an agent such as pge1 which is used to trigger the effector system .