Cordyceps (also known as ophiocordyceps sinensis) has been used in both Chinese and Tibetan medicine for centuries. A parasitic fungi that typically grows high in the mountains of Nepal and Tibet, cordyceps is highly prized for its tonic effects. 

It is said that cordyceps can boost testosterone and fertility, raise immune system function, regulate the liver, and fight cancer. It is also used to treat coughs, chronic bronchitis, high cholesterol, liver disorders, etc.[1] Cordyceps mushroom also has potent antioxidant properties[2].

 The medical research continues to grow for cordyceps sinensis. Some of the other benefits of cordyceps as tested in a clinical setting:

• Boost exercise performance^[3]
• Increase testosterone^[4]
• Cellular oxidative stress protection^[5]
• Combating altitude sickness^[6]

 References:

1. http://www.webmd.com/vitamins-supplements/ingredientmono-602-CORDYCEPS.aspx?activeIngredientId=602&activeIngredientName=CORDYCEPS&source=2  (Cordyceps - WebMD)
2. https://www.ncbi.nlm.nih.gov/pubmed/11417914 (Anti-oxidation activity of different types of natural Cordyceps sinensis and cultured Cordyceps mycelia. )
3. https://www.ncbi.nlm.nih.gov/pubmed/24047103 (Polysaccharides from Cordyceps sinensis mycelium ameliorate exhaustive swimming exercise-induced oxidative stress.)
4. https://www.ncbi.nlm.nih.gov/pubmed/21512251 (The in vivo and in vitro stimulatory effects of cordycepin on mouse leydig cell steroidogenesis)
   
5. https://www.ncbi.nlm.nih.gov/pubmed/16608242  (Comparison of protective effects between cultured Cordyceps militaris and natural Cordyceps sinensis against oxidative damage)
6. https://www.spandidos-publications.com/10.3892/mmr.2014.2786 Purification of polysaccharides from Cordyceps militaris and their anti‑hypoxic effect