Effects of Yohimbine and Naltrexone on Sexual Function

Erectile dysfunction (ED) is a relevant medical and psychological problem for males, and is usually associated with increased age. There is substantial evidence available suggesting that noadrenergic and opiate transmitter systems are involved in regulation of sexual function. The objective of the present study is to evaluate the effects and safety of a potential novel treatment combination for ED consisting of both, the alpha-adrenoreceptor antagonist yohimbine, and the opiate antagonist naltrexone. The study uses a three-phase, double-blind, placebo-controlled cross-over design. Healthy, male volunteers will participate. The effects of differing dosages of yohimbine (10 mg versus 20 mg) and a fixed dose of naltrexone (50 mg) on penile tumescene and rigidity, and sexual arousal are assessed in a placebo-controlled design. The anticipated risks of the study are considered minimal in relation to the importance of our increased knowledge about regulation of physiological and psychological aspects of regulation of sexual function and dysfunction. This novel treatment combination could be later also applied to patients with ED of different origin, e.g. organic, psychogenic, and mixed causes.

Inclusion criteria

Subjects must be medically healthy and free of mental illness, take no medication, and must report no problems with their sexual function. They are required to be sexually active, including successful penetrative sexual intercourse acts.

For assessments of sexual function before and after the study subjects are required to complete a detailed daily diary recording their erectile activity for 7 days before the first study session, and for 7 days after completion of the study.

Exclusion criteria

Persons having taken antidepressant or other medications likely to alter monoamine neurochemistry or cerebrovascular and cardiovascular function within 6 months prior to the study will be excluded.

Individuals will also be excluded if they have: a) evidence for an axis I psychiatric disorder (DSM-IV criteria), b) medical or neurological illnesses likely to affect physiology or anatomy, c) a history of drug (including BZDs) or alcohol abuse within 1 year or a lifetime history of alcohol or drug dependence (DSM IV criteria), d) smokers, e) diagnosis of a sexual disorder, f) criminal history.

Persons must exhibit no or only moderate alcohol use. Persons with current or previous regular use ( more than 4 weeks) of BZDs and excessive use of alcohol (more than 8 ounces/day) in the past or presence are ineligible to participate, as such drug use confound the results.

Individuals beyond age 50 are excluded because subjects beyond age 50 have a far greater likelihood of showing subtile, albeit clinical irrelevant disturbances in erectile function.