Letrozole is an extremely powerful anti estrogen. It also reduces progesterone since it is a form of estrogen. The problem is it is so effective at reducing(almonst all) estrogen in such small doses that it is hard to measure its anti progesterone qualities. That's why seperate anti progesterones are generally used. I've seen numbers suggesting Letro is about 40-60% as effective at reducing progesterone as it is for reducing estrogen.
If you decide to run estrogen protection while on cycle (and I suggest you do unless you are aware that you do not require it), you can run either a SERM or an AI. Letro will be the most powerful AI you can use, it will inhibit 98+% of estrogen using a dose as low as .25mg and even lower. Do not use a dose higher than .50mg while on cycle just trying to prevent estrogen related side effects.
Also we are talking about estrogen gyno here, not progesterone but using letro will stop progesterone related problems since it inhibits all estrogen. Progesterone gyno will be enlargement of your nipple area, the actual areola, not a lump under it.
