Last month (Aug 2017) a study called “Evaluation on quality consistency of Ganoderma lucidum dietary supplements collected in the United States” was published.
Nineteen Reishi (Ganoderma lucidum) dietary supplements were purchased, in February or March 2015, directly from general e-commerce sites such as Amazon and eBay in the United States. One -authenticated- Reishi fruiting body was used as a control.
The outcome was unexpected – ah well, let’s just say it, it was shocking!
All products were tested for triterpenes, polysaccharides and beta-glucan, and on top of that for authenticity (is it really Reishi?).
Only 8 of the 19 products contained triterpenes that were actually Reishi triterpenes or something at least quite close to that.
Starch-like polysaccharides (alpha-glucans) are used a lot as excipients / flow agents or fillers in dietary supplements. They are also used to ‘spike’ mushroom supplements that use ‘polysaccharides’ as a potency marker. ‘Polysaccharides’ are not reliable as a quality marker – most polysaccharides are not bioactive and the percentages can be manipulated easily.
Starch is also present in large quantities if the a mushroom supplement is not produced from fruiting bodies but from mycelium grown on grains/rice (= substrate) – the undigested substrate is starch. It has no therapeutic potential.
Normally speaking a Reishi fruiting body is starch-free after having been extracted. However, it is no longer a secret that the majority of US-produced mushroom products are not based on fruiting bodies but on biomass (the combination of mycelium and the substrate it grows in). The outcome of this study seems to confirm that once again: only 6 of the 19 products were starch-free.
Beta-glucans are the other main bioactive ingredients in Reishi. The paper found only 5 of the 19 products contained beta-glucans. When tested for authenticity, the same 5 products tested as being authentic.
A final test was determining the molecular weight of the beta-glucan fractions and to use this as a quality marker. Previous papers have shown that these high molecular weight beta-glucans are the most bioactive fractions and are suitable to be used as a quality marker. Again, only 5 out of 19 products contained this marker compound.
This study shows the quality consistency of Reishi dietary supplements collected in the USA was extremely poor.
The full text can be read here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552695/
medicinal mushrooms - backgrounds and monographs 
Is there a list of available of the tested brands?
No, the idea was to improve the quality awareness in both consumers and the industry, not to reveal cheating sellers. We contacted the writer but he would not reveal anything.