Yohimbine is an alpha-adrenoceptor blocker that has been used in the treatment of erectile dysfunction. Adequate trials of this substance in a clearly defined organically impotent population are not available. We conducted a randomized, controlled study with partial cross-over of yohimbine versus placebo in 100 organically impotent men. The first phase of the study showed a positive response in 42.6 per cent of the patients receiving yohimbine versus 27.6 per cent in the placebo group. Although favorable to the test medication these values did not reach statistical significance (p equals 0.42). A similar pattern was noted in the second phase of the study. The over-all response rate of 43.5 per cent was consistent with a previous noncontrolled trial but it was much lower than previous studies. The response rate of organically impotent patients to yohimbine is at best marginal. Owing to its ease of administration, safety and modest effect it still is used in those patients who do not accept more invasive methods. Adrenoceptors are involved in the erectile process, although other neurotransmitter systems also are putative modulators of penile erection, including cholinergic, dopaminergic and vasoactive intestinal polypeptide pathways. It is beyond reasonable expectation that a single agent be of value for all cases of organic impotence. However, yohimbine has shown modest effectiveness at the doses used in this trial (18 mg. per day). Higher doses or a different route of administration may produce different effects.

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