McKennaii mushrooms are a strain of Psilocybe cubensis, one of the most commonly used species of psilocybin mushroom. The latter is a medium-strength magic mushroom, whereas McKennaii mushrooms — like many other strains of Psilocybe cubensis — are very potent. This means that they contain higher concentrations of the compounds psilocybin and psilocin, which are responsible for psychedelic effects.