depending on weather people are pre-disposed to gyno, genetically, natural test boosters can cause an aggravation in gyno. this was something that did have potential, however slight, with the original mass fx and activate. with the new ones of each of these products there has been advancement in the sense that they each can easily be ran stand alone with thanks to the inclusion of estrogen blockers in each product. if it is a huge worry than i would recomend an estrogen blocker like hyperdrol 2 to ease your worries and to add synergetic effect as well