Mushroom Science Coriolus PSP is available in a 90 capsule size. Polysaccharide-peptide is a recent addition to the family of medicinal-mushroom-extract products. Developed in China, extensive clinical testing did not begin until the early 1990s. Under NMR analysis the glucan portion of PSP is almost identical to that of PSK and VPS, however, due to variations in fermentation media and extraction methods, there are some differences. PSP contains arabinose and rhamnose as single sugars but no fucose. The material used in the Japanese research (PSK) and VPS contain protein in the non-polysaccharide portion of the molecule, PSP contains peptides.