Horny Goat Weed for Erectile Dysfunction

February 2001; Volume 4; 19-22

By Michael D. Cirigliano, MD, FACP, and Philippe O. Szapary, MD

Coupled with the fact that many men still feel uncomfortable discussing erectile dysfunction (ED) with their doctors, alternative and "natural" treatments for ED are widely sought. Agents including yohimbe, arginine, Avena sativa, and muira puama are employed extensively, though most lack significant scientific data on safety and efficacy.

The herbal agent horny goat weed (Epimedium sagittatum, family Berberidaceae), along with several other Epimedium species, now joins this group, with a twist. With its suggestive name, the use of horny goat weed is on the rise across the United States and abroad both for ED and as an aphrodisiac. Its rise in popularity and desirability have in fact made it a high-theft item, requiring horny goat weed to be kept under lock and key in many health food stores and pharmacies. Anecdotes and testimonials, sometimes by celebrities, have led many to consider horny goat weed to be the new age "natural viagra."

Background: Erectile Dysfunction

ED is a common disorder affecting men of all ages. The prevalence of some level of ED has been estimated to be approximately 40% in men at the age of 40, and as high as 67% in those at the age of 70.1 Pharmaceutical agents, along with a number of other modalities, have been developed and are available for treatment, but they are not without side effects and significant cost. Some agents are contraindicated for men with common medical conditions. In many cases, these agents may not be covered by insurance carriers.

Etymology

The term "horny goat weed" is thought to have originated from the observation that goats consuming the plant became much more sexually active than normal. It is also known as "Yin-yang-huo."

Chinese Medicine

Horny goat weed has warming properties and is pleasant to the taste.2 According to traditional Chinese medicine principles, it is said to warm the kidneys, to strengthen the yang element (virility), and to remove excess moisture and flatulence. Horny goat weed was described in The Herbal Classic of the Divine Plowman as a bodybuilding agent, a yang supporter, an agent to reinforce muscles and bones, and a help to the liver and kidney.3

Historically, horny goat weed has been used medicinally for a wide variety of ailments including impotence, involuntary ejaculation, fatigue, coronary artery disease, kidney disease, chronic hepatitis, and polio.4

Source and Identification

A perennial evergreen indigenous to China and Japan, the herb is found growing on hillsides, in damp shady bamboo groves, or in cliff crevices.2 The leaves are used medicinally, usually in a decoction. In the spring, light yellow terminal flowers appear. The herb is collected in the summer and autumn, mainly in the provinces of Shaanxi, Liaoning, Shanxi, Hubei, Sichuan, and Guangxi.5

At least 15 Epimedium species have been identified. The dried aerial leaves of a number of species, most commonly including E. grandiflorum, E. sagittatum, E. pubescens, E. wushanesis, or E. koreanum, are used.

Pharmacology

Horny goat weed contains a number of active constituents including flavonoids (more than 20 identified), lignans, phenol glycosides, ionones, sesquiterpenoids, and phenethylol glycosides.5 It is believed that the active principal components include the glycosides icariin and noricariin.3 In addition, ceryl alcohol as well as some essential oils and fatty acids may play an active role in the pharmacological properties of horny goat weed.

Mechanism of Action

Increased male sexual function appears to arise from horny goat weed’s peripheral vasodilatory and hormonal effects.3 One study noted that icariin had calcium
channel-blocking activity, leading to vasodilation.6 It is believed that the hypotensive effect of the herb may be related in part to the blockade of sympathetic ganglia, in addition to its effects on calcium channels.7,8

The herb’s glycosides also have been reported to have sexually stimulating effects on male mice and rats by promoting semen secretion and by stimulating the growth of the prostate, testis, and anus rector muscles.7 Increases in urinary excretion of androgen precursors, including17-ketosteroids, have been observed, and some investigators believe that horny goat weed effects derive from modulation of cAMP and increased testosterone secretion. Horny goat weed also has been shown to be effective in antagonizing the impotency induced by hydrocorticosterone administration in mice.9

Other properties observed in animal studies of the herb include increased coronary blood flow and decreased platelet aggregation. Reports indicate that the glycosides of the herb can increase immune activity and act synergistically with other immune-enhancing agents to stimulate IL-2, IL-3, and IL-6.3

Animal Studies

A review of MEDLINE and IBIDS databases revealed 12 basic science-related studies. Several of these support the theory that epimedium has calcium channel-blocking activity, leading to vasodilating qualities and increased blood flow.6,10

In one of the best animal studies, the effects of epimedium extract (icariin) and another yang herb, semen cuscutae, were evaluated in 36 male Wistar mice.11 Animals were divided into four groups including a control group, those receiving a horny goat weed extract, those receiving a semen cuscutae extract, and those receiving hCG. Subdermal injections were administered for six days. Following administration, animal testes, epididymi, and seminal vesicles were weighed. Results indicated that horny goat weed extract increased the weights of the epididymi and seminal vesicles but did not have an influence on testicular weights. Semen cuscutae also was able to increase the weights of the testes and epididymi. The authors concluded that both herbs possessed androgenic hormonal activity and gonadotropin-like actions.

In another animal trial, the herbal product BetterMAN™—a combination product that contains 18 traditional Chinese herbs including Epimedium sagittatum—was evaluated in a placebo-controlled trial using rats with experimentally induced ED.12 Rats were randomized to receive a normal diet vs. a diet high in cholesterol. Eight control animals were fed a normal diet while 24 were fed a 1% cholesterol diet for four months. After two months, BetterMAN was added to the drinking water of 16 of the 24 rats receiving a high-cholesterol diet. Eight rats received daily dosages of 25 mg/kg and eight rats received daily dosages of 50 mg/kg. At four months, erectile function was evaluated with cavernous nerve electrostimulation in all animals. Results indicated that rats developed ED after being fed a 1% cholesterol diet for four months. Erectile response was significantly better in the treated group. Increased levels of basic fibroblast growth factor and caveolin-1 expression in the treated group was thought to protect the cavernous smooth muscle and endothelial cells from the harmful effects of high serum cholesterol.

Clinical Studies

Few sound clinical data describe the safety and efficacy of horny goat weed for ED or as an aphrodisiac, despite widespread use. An extensive search of the literature revealed no English language trials. Communication with members of the Herb Research Foundation, however, did identify four human clinical trials involving horny goat weed. All were in Chinese, requiring translation.

In the first of these trials, 50 patients with ED were treated with an oral, combined preparation of epimedium and semen cuscutae.13 In this case series, 50 men with ED ranging in age from 20-60 years were treated as outpatients. All patients in the study reportedly had experienced ED for seven months to 16 years. Treatment involved taking the ground powder of epimedii and cuscuta (15 g each) in a 5 g dose tid with "cooking wine." Treatment lasted on average for 20 days. In addition, supplementary treatment included perineal and genital massage as well as bathing in medicinal water and other Chinese herbs for 20 minutes every evening. Entry requirements for the study included no intercourse for 100 days prior to participation.

Results indicated that 38 patients achieved total recovery, which accounted for 76% enrolled; eight patients experienced some improvement (18%). Four patients noted no improvement (8%) for a total effectiveness rate of 92%. The treatment period ranged between seven and 48.5 days. Follow-up visits with 20 patients found no recurrence of symptoms for two years.

In the second study, 30 patients with kidney disease (17 males and 13 females) ranging from 19 to 43 years of age were evaluated.14 Patients were given "Yishen Soup," which was comprised of 12 Chinese herbs including epimedium. Patients were treated for 20 to 84 days. Improvement was defined as either resolution of clinical symptoms or improved "urine" parameters and blood urea nitrogen. Those patients having a "tendency" toward impotence were noted to have an improvement of symptoms with treatment. According to the authors, 16 cases achieved clinical recovery, with 11 showing improvement and three showing no effects.

In the third trial, the effects of epimedium on a number of clinical and laboratory parameters were evaluated in 34 patients with renal failure on hemodialysis.15 Twenty-one males and 13 females (average age of 38) were enrolled. Patients receiving epimedium were noted to have improvement in both renal and sexual function, especially patients under 40 years of age. Patients were treated for four months but were noted to show improvement even after one dose.

In the final trial, 22 hemodialysis patients were treated with an Epimedium sagittatum decoction.16 In this trial, 12 other patients receiving hemodialysis served as controls and did not receive the extract. There is no mention as to the selection of controls or a matching placebo. Techniques of blinding and randomization were not revealed. It was found that those patients in the treatment arm had "improvement" in sexual performance and an improved quality of life.

All the mentioned studies have significant limitations including small sample size, lack of uniform diagnosis, use of multiherbal preparations, use of co-interventions (massage), and lack of appropriate controls or random assignment.

Adverse Effects and Drug Interactions

Horny goat weed appears to be safe in animals when taken for short periods of time in recommended dosages. At an oral dose of 450 g/kg, normal activity of mice was not altered and toxic reactions were not observed during three days of observation. The LD50 of the concentrated decoction of the herb in mice was 36 g/kg by intraperitoneal administration.7

A manual of traditional Chinese medicine lists adverse effects; it appears that these have been observed in animals, but the source is unclear.17 Extended use of Japanese epimedium (Epimedium grandiflorum) has resulted in dizziness, nausea, vomiting, dry mouth, and nosebleed.17 Large doses of Japanese epimedium have been noted to cause respiratory arrest and exaggeration of tendon reflexes to the point of spasm.17 Given the paucity of documented safety data in humans, horny goat weed use is contraindicated in pregnancy.

No known drug interactions have been identified. Patients on vasodilating agents, however, should be aware of the theoretical possibility of hypotension when combining horny goat weed with them.

Formulation and Dosage

A number of herbal preparations utilizing epimedium alone or in combination with other herbal remedies are available. Several standardized formulations use a 5% icariin flavonoid marker. This "standardization," however, is not necessarily the active principal. The usual recommended daily dosage is between 0.5 mg and 1.5 mg.

Conclusion

Unfortunately, most of what is known about horny goat weed comes from basic science studies and involves human data from inadequate case series. Given the limited amount of human data available regarding epimedium for ED and as an aphrodisiac, its use cannot be recommended. Its rising acceptance in the U.S. population is concerning, given the Epimedium species’ vasodilating properties, which may be contraindicated in patients on antihypertensives and nitrates. A randomized clinical trial is needed to help clarify the value of this popular herb.

Recommendation

Based on the present data, the use of horny goat weed for ED or as an aphrodisiac should be discouraged. Primary care providers should focus their efforts on screening their patients for ED and use standard, effective, proven therapies.

Dr. Cirigliano and Dr. Szapary are Assistant Professors of Medicine at the University of Pennsylvania School of Medicine in Philadelphia.

References

1. Feldman HA, et al. Impotence and its medical and
psychosocial correlates: Results of the Massachusetts Male Aging Study. J Urol 1994;151:54-61.

2. Hu-nan Chung i yao yen chiu so. Ko wei hui. "Yin Yang-huo." In: A Barefoot Doctor’s Manual. Philadelphia, PA: Running Press; 1977.

3. Huang KC. Yin Yang Huo. In: The Pharmacology of Chinese Herbs. Boca Raton, FL: CRC Press; 1999.

4. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley and Sons; 1996.

5. Zhu, XP. Yin Yang Huo. In: You-Ping Zhu. Chinese Materia Medica: Chemistry, Pharmacology and Applications. Amsterdam: Harwood Academic Publishers; 1998.

6. Gua LX, et. al. Calcium channel blocking effects of icariin. Chin Pharmacol Bull 1996;12:320.

7. Wang YS. Pharmacology and Applications of Chinese Materia Medica. Beijing: People’s Health Publisher; 1983.

8. Xu JP, Xu RS. Phenyl glycosides from Curculigo orchioides [in Chinese]. Yao Hsueh Hsueh Pao 1992;27:353-357.

9. Sun PY, et al. Structure determination of korepimedoside A and korepimedoside B from Epimedium koreanum Nakai [in Chinese]. Yao Hsueh Hsueh Pao 1996;31:602-606.

10. Wang M, et al. Effects of Epimedium icariine on rabbit and dog vascular smooth muscle. J Shenyang Coll Pharmacy 1993;10:185-190.

11. Xiong Y, Zhou C. The effect of extracts from epimedii and semen cuscutae on the function of male reproduction. Zhongguo Yaoxue Zazhi 1994;29:89-91.

12. Bakircioglu ME, et al. Effect of a Chinese herbal medicine mixture on a rat model of hypercholesterolemic erectile dysfunction. J Urol 2000;164:1798-1801.

13. Yin A, et al. Successes in the treatment of impotence with a combination of epimedii and cuscuta yun nan. J Tradit Chin Med 1989;10:13.

14. Yong C. 30 cases of treatment of chronic kidney disease with YISHEN soup. I Chieh Ho Tsa Chih 1990;10:262, 292-294.

15. Chen X, et al. Effect of Epimedium sagittatum on soluble IL-2 receptor and IL-6 levels in hemodialysis [in Chinese]. Chung Hua Nei Ko Tsa Chih 1995;34:
102-104.

16. Liao HJ, et al. Effect of Epimedium sagittatum on quality of life and cellular immunity in patients of hemodialysis maintenance [in Chinese]. Chung Kuo Chung His I Chieh Ho Tsa Chih 1995;15:202-204.

17. Bensky D, Gamble A. Chinese Herbal Medicine. Seattle: Eastland Press, Inc.; 1986.