Nolvadex (brand name for Tamoxifen) like all SERM medications and aromatase inhibitors has the ability to increase erections and libido or kill both of them stone dead.
It all depends upon the initial level of estradiol, the dosage involved and ultimately how it affects the amount of estradiol able to work in your endocrine system.
If there is too much estradiol able to work in your system you have Ed and libido issues, too little and yuou have the same problem.
So it is about having the right amount of estradiol in your body in order to function correctly.
It is key that pathology highlights a need for such medcations prior to use. If you have ED and a low libido that might be down to a whole host of causes, low testosterone or thyroid hormone fro instance, it is not neccessarily down to elevated E2. If you just assume you have a high level of E2 and throw Nalvadex at it then you can end up with too little estradiol able to work in the body and make matters worse.
P.S
It is difficult to dose Nolvadex and SERM medications because estradiol blood test are rendered useless given the fact that they do not lower estradiol in the blood but block its action and the estrogen receptor sites. If aromatase inhibitors are used, then estradiol is lowered in the blood and an estradiol blood test can be used to correctly alter dosing. That said Nolvadex is useful in other regards and can be the right tool in the hands of a competant endocrinologist.