To be fully effective, the medications must be injected directly into 1 of the penile erectile bodies, the corporus cavernosum. The medication will diffuse over to the other side of the penis so that symmetrical erection is achieved. A cross section of the penis shows the relationship of the site of injection to the corpora cavernosae. Most males use an insulin syringe with a 26- to 30-gauge 1/2-inch needle.
