The purpose of this study is to evaluate the safety and effectiveness of the drugs yohimbine
and naltrexone in treating men with erectile dysfunction (ED) (the inability to achieve or
maintain penile erection for satisfactory sexual performance).
ED is a medical and psychological problem that is usually associated with increased age.
Evidence suggests that specific neurotransmitter systems are involved in the regulation of
sexual function. Yohimbine and naltrexone are drugs that may influence these
neurotransmitter systems. This study will use different doses of yohimbine and fixed doses
of naltrexone to determine their effectiveness in treating ED.
Participants in this study will be screened with a medical history, physical examination,
blood and urine tests, and an electrocardiogram (ECG). The study will consist of three
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.
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.
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