This is probably one of the most important pieces of information to find out, since it directly affects the quality of the product. Mycelium grown on grain is a cheap way to mass produce mushroom supplements, however these products do not have the same benefits as naturally cultivated mushrooms. Make sure your product label shows that it is made of real mushroom, not mycelium. Most companies will be honest about mentioning whether it is a mycelium grown on grain product, however, some packaging may be confusing and designed to make you think it is a natural mushroom product when in fact, it is not. To be safe, do your due diligence and thoroughly research the products, and their manufacturers before taking them. This goes for any supplement, not just medicinal mushrooms.
Surprisingly, the FDA states that mycelium products cannot be labeled as mushrooms (Compliance Policy Guide, Section 585.525.). However, some companies defy this regulation.