Since I have copy and pasted this reply in PM's over and over I thought I would post it so it's easy to find in a search. It's an Aromatase Inhibitor. The "feedback loop" that your HPTA (brain) uses to signal your testes to make more testosterone measures how much estrogen is in your blood. It doesn't measure how much testosterone there is. So when it sees low estrogen it signals for more testosterone, that's the feedback loop. Where does the estrogen come from? That's the key. Estrogen comes from Testosterone (for the sake if this discussion we aren't going into the other smaller sources of estrogen). An enzyme called the Aromatase enzyme makes estrogen out of Testosterone. So if you have Testosterone pumping up out of your testes, the aromatase turns it into Estrogen, the HPTA reads the estrogen levels and when it gets too high it shuts off the testes. When the levels of Estrogen get low it turns them back on. AIFM attaches to the aromatase enzymes and kills them. With less aromatase to convert your Testosterone into Estrogen, your blood level of estrogen drops. Your HPTA reads that there is low Estrogen and signals the testes to make more Testosterone. Then that Testosterone doesn't get converted and so on. You're tricking your brain into thinking you have less Testosterone than you do so it keeps pumping it out of your testes. AIFM = Dead Aromatase = higher natural testosterone levels.