While most think of Viagra when they think of erectile dysfunction, there are many natural herbs that are used to treat the problem too. In Chinese medicine, Ginkgo biloba is widely prescribed. But a new study has found that the herb, along with many other “natural” ingredients found in over-the-counter supplements sold to improve male sexual health, lack strong scientific evidence of benefits. Some could even be harmful. SEE ALSO: Penis size: the long and the short of it “While certain natural supplements we reviewed show promise for improving mild sexual dysfunction, they lack robust human evidence,” says Dr Ryan Terlecki, associate professor of urology and senior author of the study, published online in the Journal of Sexual Medicine. “In addition, because of concerns that some products are impure or weak, we do not routinely recommend these products to our patients.” An estimated 40 to 70 per cent of men experience some form of sexual dysfunction during their lives. Terlecki and his colleagues at Wake Forest Baptist Medical Centre in North Carolina looked at scientific evidence for the most common and top-selling “natural” supplements were effective and safe. For some products, such as Horny Goat Weed (Epimedium), no scientific evidence was found to support claims that it has any effect on erectile function, libido and sexual performance. Some products that are advertised as being “natural”, contain traces of phosphodiesterase-5-inhibitors (PDE5Is), the same class of medication as prescription drugs such as Viagra. One study revealed that 81 per cent of tested samples of over-the-counter products purchased in the US and Asia contained PDE5Is. “Men who use these medications without a physician’s supervision run the risk of taking them inappropriately,” says Terlecki. “Patients with advanced heart disease, for example, or who take nitrates, such as nitroglycerin, should not use PDE5Is as it may cause an unsafe drop in blood pressure. Likewise, men with severe liver impairment or end-stage kidney disease requiring dialysis should avoid these products.” Here is a summary of some of the authors’results: * DHEA (a steroid hormone) seems relatively safe as the data does not show any significant impact on hormone levels. The data is too weak to suggest a benefit. * Fenugreek is seen in about a third of the top-selling men’s health supplements. One study noted a benefit in improving sexual arousal and orgasm, as well as muscle strength, energy and well-being. There were no adverse events reported in that study and other studies also show this to be a safe supplement. * Ginkgo biloba has been marketed to treat numerous conditions. There is no convincing data to support its use for erectile dysfunction. It can cause headaches, seizures and significant bleeding, especially if patients are taking the anticoagulant Warfarin. * Ginseng is the most common ingredient in top selling men’s health supplements. It can cause headache, upset stomach, constipation, rash, insomnia and can lower blood sugar (possibly problematic for diabetics). * Horny Goat Weed is generally safe with rare reports of toxicity (fast heart rate and hypomania). There is no evidence in humans of any benefit in sexual function. * L-arginine is the most common amino acid seen in men’s health supplements, also in about a third of top sellers. It has the theoretical potential to improve erectile function in some patients and seems relatively safe. It has been associated, however with a drop in blood pressure, but without a significant change in heart rate. * Maca is the most common vegetable among top selling men’s health supplements. In animal research, use of maca was associated with increased sexual behaviour. There have been rare reports of toxicity, such as a mild increase in liver enzymes and blood pressure. * Tribulus has no evidence of benefit in humans. Two reports of liver and kidney toxicity in young men taking high doses of extracts of this plant. * Yohimbine has shown promise for improving male sexual function in some studies. The drug (derived from the bark of an African tree) has been used for a long time. It can cause hypertension, headache, agitation, insomnia and sweating. * Zinc appears to be safe, but there is no evidence of benefit in normal individuals.