Epimedium, commonly known as "Horny Goat Weed," has a long history of use in traditional Chinese medicine (TCM) as a remedy for erectile dysfunction (ED) and low libido. The herb is believed to enhance sexual function and vitality, particularly in men. Its use is documented in classical TCM texts, where it is described as a kidney tonic that strengthens "yang" energy, which is associated with sexual health and performance in TCM theory.

From a scientific perspective, there is some preliminary laboratory evidence that Epimedium contains icariin, a compound that may have phosphodiesterase type 5 (PDE5) inhibitory activity, similar to how sildenafil (Viagra) works. However, robust clinical trials in humans are lacking, and the available studies are generally of low quality, small sample size, or conducted in animals. Therefore, while the mechanism is plausible based on in vitro and animal research, there is insufficient high-quality clinical evidence to substantiate its efficacy for ED in humans.

In summary, the use of Epimedium for erectile dysfunction is primarily justified by traditional use, with some supportive but not definitive scientific rationale. The overall quality and quantity of scientific evidence supporting its effectiveness for ED remain limited.