Drug Interactions

When taken with medications that thin your blood or prevent clotting, horny goat weed may increase your risk of developing prolonged or uncontrollable bleeding following an injury or surgery, reports RxList. Drugs that may cause this reaction include captopril, enalapril, losartan, valsartan, diltiazem, amlodipine, hydrochlorothiazide and furosemide.

Time Frame

Side effects and risks of horny goat weed are most likely to occur at high doses or with long-term use, such as taking the herb continuously for more than two years, reports RxList.

Clinical Evidence

A Chinese study conducted in 1989 by M.D. Chen, A.K. Kuang and J.L. Chen and published in the Chinese Journal of Modern Developments in Traditional Medicine found that horny goat weed decreased the production of thyroid hormones in laboratory animals. There has not been a similar study to determine if this effect is possible in humans.

Risks

Possible side effects of horny goat weed include dizziness, vomiting, dry mouth, thirst, nosebleeds, muscle spasms and serious breathing problems, reports RxList. Other possible effects include aggressiveness, irritability, fever and rapid heartbeat, according to the University of Michigan Health System.

Considerations

Because its effects upon fetal development are unknown, avoid taking horny goat weed if you are pregnant or nursing. If you have a history of low blood pressure, it may not be safe for you to take horny goat weed, cautions RxList.

Source:

RxList: Epimedium Effectiveness, Safety and Drug Interactions

University of Michigan Health System: Horny Goat Weed

Pubmed.gov: Influence of Yang-Restoring Herb Medicines upon Metabolism of Thyroid Hormone in Normal Rats and a Drug Administration Schedule