Nutrition Action Healthletter
Center for Science in the Public InterestJuly/August 2000 — U.S. Edition 
Peddling Potency
Do Impotence Busters Work?
The Bottom Line

There is little scientific evidence that avena sativa, damiana, ginseng, ginkgo biloba, maca, muira puama, or zinc can improve libido or sexual function.

There is some evidence that arginine helps some men. So does yohimbine, a prescription drug that may or may not be present in yohimbe supplements.

There is no good published evidence that any dietary supplement can improve libido or sexual function in women.

Sex and the Heart

“If it’s a bad habit for your heart, it’s probably bad for your sex life too,” says epidemiologist Henry Feldman of the New England Research Institute in Watertown, Massachusetts.

Feldman and his colleagues recently re-examined 513 middle-aged men nine years after enrolling them in the Massachusetts Male Aging Study.1 All were free of heart disease, diabetes, and erectile difficulties when they joined the study. But nine years later, 14 percent had become moderately or completely impotent.

“The cigarette smokers were nearly twice as likely to experience erectile dysfunction (ED) as those who didn’t smoke,” says Feldman. “Being exposed to a double dose of passive smoke — at home and at work — also doubled the risk,” he adds.

The other risk factor for impotence: a Body Mass Index (BMI) greater than 28. (Your BMI is 28 if you’re 5’6” tall and weigh 173 lbs. It’s also 28 if you’re 153 lbs. at 5’2”, 163 lbs. at 5’4”, 184 lbs. at 5’8”, or 195 lbs. at 5’10”.)

Feldman’s study didn’t find any connection between high blood cholesterol and erectile difficulties. But in an earlier study of more than 3,000 Texans, for every 40 points higher a man’s total cholesterol, his risk of developing erectile dysfunction during the next two years increased by 32 percent.2 Lower HDL (“good”) cholesterol was also linked to ED.

Why? High cholesterol can lead to clogged arteries...and not just ones that feed the heart. Israeli researchers found, for example, that men with serious blockages in two of their coronary arteries were likely to experience more erectile difficulties than men with only one blocked artery.3

“Our new data tighten the noose of evidence suggesting that at least some of the risk factors for cardiovascular disease are also risk factors for ED,” says Feldman.

And women? “Blood flow is important for women too,” adds Feldman. “Since we know that what’s bad for men’s hearts is also bad for women’s hearts, it would follow that tobacco smoke, being overweight, and perhaps having high cholesterol levels would interfere with women’s sexual function too.”

1: Prev. Med. 30: 328, 2000.
2: Am. J. Epidemiol. 140: 930, 1994.
3: Internat. J. Impot. Res. 9: 123, 1997.

Potency’s in. And dietary supplement manufacturers don’t want to miss out. They’re no dummies. They know that Viagra was the best-selling new drug in history, and that at $10 a pill, it continues to be a pharmaceutical superstar.

   So how can an enterprising supplement-maker get in on the action? Take some herbs or other compounds that have traditionally been used as aphrodisiacs and slap an eye-catching label on them. Call them Aroused, or maybe Climaxx, or Instant Sex, or Love in a Jar, or Libidoblast, or NiAgra.

   Who cares if there’s little scientific evidence? Your product is “natural,” it doesn’t need a prescription, and it’s much cheaper than Viagra. You can even bottle women’s formulas (though just about all of the research is on men or male animals). And, best of all, you don’t have to worry about nosy government regulators. Nobody’s forcing you to disclose that your product probably hasn’t been tested for safety. And who knows whether it interferes with prescription drugs? The feds aren’t paying attention.

   The evidence for potency supplements is not as reliable or clear-cut as it is for Viagra. (In one study, for example, 69 percent of all attempts at intercourse by Viagra-takers were successful, compared to only 22 percent by placebo-takers.)

   We found more than 150 impotence-busting, libido-boosting supplements for sale in catalogs and on the Internet. Most (including those shown in our photos) contain one or more of nine ingredients. Here’s what we know about each of them.

   It’s an amino acid that can raise levels of nitric oxide in the blood and body tissues. That can increase blood flow, which is necessary for arousal. At least that’s the theory. Only two small published studies have looked at whether arginine has any effect on sexual performance in humans. In both cases, the results were less than spectacular. In one, at New York University, Eli Lizza and the late Adrian Zorgniotti gave 15 men with erectile dysfunction a placebo for two weeks, then 2,800 mg of arginine every day for two weeks.1 Six (all under age 44) noticed an improvement with arginine; none with the placebo. But Zorgniotti couldn’t duplicate the results in a subsequent study, Lizza recalls.

   In the second published study, researchers at Tel Aviv University in Israel gave 46 men with erectile dysfunction either 5,000 mg of arginine or a placebo every day for six weeks.2 Arginine made no difference in erectile function or sexual activity, performance, or satisfaction, according to questionnaires filled out by the men. What’s more, the researchers could detect no increased engorgement of the arginine-takers’ genitals. Yet nine of the 29 arginine-takers (versus two of the 17 placebo-takers) reported a “significant” improvement in their sex lives. Go figure.

   Two not-yet-published studies have looked at ArginMax, a combination of arginine, ginkgo, ginseng, a handful of vitamins, and (in the women’s formula) damiana. In one, 21 of 24 men with erectile dysfunction who took ArginMax for four weeks reported improvement in their ability to maintain an erection during intercourse, compared to five of 24 men who were given a placebo. In the other study, 25 of 34 women who took ArginMax for four weeks reported that their sex lives were more satisfying, compared to 16 of 43 women who were given a placebo. Until the studies are peer-reviewed and published, there is no way to know if the results are valid.

1: Internat. J. Impot. Res. 6: 33, 1994.
2: Brit. J. Urol. Internat. 83: 269, 1999.

Avena Sativa
   Most claims for the oat extract rest on research conducted during the 1980s by the Institute for Advanced Study of Human Sexuality in San Francisco, which markets a line of avena sativa products. The one study on men and women that compared avena sativa to a placebo was never published, says Institute head Ted McIlvenna, “in part because we didn’t want our competitors citing it to sell their own products.”

   But that hasn’t stopped erroneous accounts of the research from circulating. A typical example, from advertising for an anti-impotency supplement: “The 38 men who completed the study experienced improved sex drive, firmer erections, speedier arousal, and greater pleasure during sex when taking avena sativa than when on placebo.”

   Yet when you analyze a summary of the study provided by McIlvenna, it’s impossible to tell whether there was any meaningful difference between the avena-sativa-takers and the placebo-takers. One finding was clear, though. The 25 women who completed the study did better on the placebo. McIlvenna says that as a result of the study, the Institute reformulated its product for women. But he declined to release the details of a second study, in women only, that he claims shows that the reformulated product works.

   The libido-boosting power of damiana — which is extracted from the leaves of a shrub native to Latin America — hasn’t been tested in humans, although a liquor made from the leaves has long been used as an aphrodisiac in Mexico. In animal studies, extracts of damiana speeded up the mating behavior of “sexually sluggish” or impotent male rats last year. It had no effect on sexually potent rats.

   Ginkgo may improve circulation, and several studies have shown that it can help with sexual function. But none of them compared the herb to a placebo, so there’s no way to tell whether the improvement would have occurred no matter what the participants were given. The most recent study gave 300 mg of ginkgo to 22 men and women who had sexual complaints as a result of taking antidepressants. After one month, none of the nine complaints by the men, and only four of the 31 complaints by the women, had diminished.1

1: Amer. J. Psychiatry 157: 836, 2000.

   There is some evidence that the traditional Asian aphrodisiac may generate more nitric oxide from arginine, which could lead to increased blood flow and arousal. In the only good published study, 30 Korean men with erectile dysfunction who took 1,800 mg of Korean red ginseng every day for three months were more likely to report greater sexual desire and erectile function than 30 similar men who took a placebo.1 But researchers couldn’t corroborate the improvement in the laboratory. They could detect no increased engorgement of the ginseng-takers’ genitals.

   Korean red ginseng is produced by a special steam process. Asian and Siberian ginseng, the kinds most commonly found in supplements, have never been tested in good published research on libido or sexual performance.

1: Internat. J. Impot. Res. 7: 181, 1995.

   It’s the root of a vegetable that is eaten or made into a fermented drink in the Peruvian Andes, where it has been cultivated for more than 2,000 years. The only good study showing any effect of maca on libido or sexual performance is in rodents. Feeding high dosages of two maca extracts to normal male mice tripled the frequency with which they coupled with female mice. It also reduced by half the time that rats with erectile dysfunction needed between successive couplings.

Muira Puama
   “In less than 2 weeks, 70% of patients treated with muira puama claimed a dynamic improvement in sexual performance.”

   Dozens of supplement manufacturers repeat the same tale about the extract from a bush native to northern Brazil that has traditionally been used as an aphrodisiac. Yet the only two studies on muira puama have never been published. We can see why. They didn’t test it against a placebo.

   Yohimbe is an over-the-counter supplement made from the bark of a West African tree that has traditionally been used to treat fever, coughs, and leprosy. Yohimbine, a compound extracted from the bark, is a prescription drug approved by the Food and Drug Administration (FDA) to dilate (widen) the pupils of eyes.

   Since yohimbine can cause blood vessels to dilate and blood flow to increase, some physicians prescribe it for erectile dysfunction. And there’s some evidence that it works. In a 1997 meta-analysis that pooled the results of seven good studies, 15 to 43 mg of yohimbine every day for four to ten weeks was more effective than a placebo in helping many men who were suffering from one or more sexual dysfunctions.1

   But the meta-analysis couldn’t determine which conditions were helped and which weren’t. And two later studies found no benefit from yohimbine.2,3 What’s more, in 1995 the FDA found little or no yohimbine in 11 of 18 brands of yohimbe supplements. And none of the other seven brands contained anywhere near the amount of yohimbine that was used in the good human studies.

   “Some supplement companies may have been buying their yohimbe from flavor-extract manufacturers, whose products don’t contain yohimbine,” explains Joseph Betz, who conducted the FDA study. Betz is now with the American Herbal Products Association, a trade group.

   Then there are the side effects. Yohimbine can raise blood pressure, and the FDA cautions physicians to be careful when prescribing it for people with a history of heart disease, high blood pressure, or kidney disease. Nobody has looked at whether yohimbe supplements also raise blood pressure.

1: Journal of Urology 159: 433, 1998.
2: Urology 49: 441, 1997.
3: Journal of Urology 159: 122, 1998.

Zinc is essential for normal sexual development during male adolescence and for producing healthy sperm. Unfortunately, only two good studies have tested zinc supplements on sexual function, and both involved a total of 17 men on dialysis for kidney disease. The men in one of the studies reported improved potency when zinc was added to their dialysate fluid.1 The men in the other study reported no improvement.2 Whether zinc can help healthy men is unknown.

1: Lancet 2: 895, 1977.
2: Lancet 2: 618, 1980.

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