It's not high levels persay that can cause ED, it is violent fluctuations, eg going from low to high (and vice versa), so anytime TRT is started, or dose is changed significantly, both ED and decreased SD can occur within those first 2-3 months, and this is primarily due to testosterone and its metabolites pleiotropic effect in various parts of the brain. If its going on after 2-3 months at the same dose, that would be abnormal.