The boom in "medicinal" mushrooms

They're called reishi, lion's mane, maitake or cordyceps and they promise immunity, concentration, well-being or energy. Sold as powders, capsules, drops, cocoa or coffee drinks, these mushroom-based dietary supplements are all the rage. Their proponents also claim that they are effective against certain cancers, liver and cardiovascular problems, and lower cholesterol. But what are we to make of the seductive promises of what is known as "mycotherapy"?