The active ingredient in Marvlix may increase the symptoms of autoimmune disorders and slow blood clotting, which increases bleeding risk after surgery and for patients who have bleeding disorders, according to WebMD. Since Marvlix may increase the activity of the immune system, patients with lupus, multiple sclerosis and rheumatoid arthritis may see their conditions worsen while on Marvlix. Nausea, diarrhea and dry mouth are also side effects, notes Drugs.com.
Cordyceps, the main ingredient in Marvlix, is generally considered safe, according to Drugs.com. In studies involving mice, researchers were unable to establish a lethal oral dose. Animal studies do show that the fungus can affect plasma testosterone levels and cause an upregulation of the immune system. However, as of 2015, there have been few well-controlled clinical human trials of the drug.
Many of the human trials that do exist were conducted using poor methodologies, making it difficult to draw definite conclusions about the drug, states Drugs.com. Some trials tested combination products, which makes it difficult to isolate the effects of Cordyceps itself.
Many clinical studies also have uncertain dosing, since many herbal supplements contain differing and undisclosed amounts of Cordyceps. For example, Elixir Industries, the manufacturer of Marvlix, claims to use a special extraction process that yields a product with a higher concentration of the active substances in Cordyceps fungus.