While both MAO-A and MAO-B metabolize tyramine, only MAO-A is present in the gastrointestinal tract and singularly metabolizes the majority of consumed tyramine.[4] (The small portion normally passing into circulation is mostly degraded in the liver where both MAO types act.[4]) Consequently, MAOIs that irreversibly inhibit MAO-A will permit high levels of circulating tyramine able to cause tyramine-induced hypertensive crisis. Aged cheese, beer, red wine, some mushrooms, and fermented products such as pickles are foods containing high levels of tyramine that passed into circulation can cause such a hypertensive crisis.