Dopamine, Testosterone, and Sexual Function
We could fill this entire website with research articles on dopamine and sexual function. Dopamine is the central player in sexual desire, erections, sexual fetishes and sexual addictions. When a porn user asks why they have sexual dysfunctions - the answer is dopamine. One of the most common complaints is erectile dysfunction, which is due to overstimulation of the reward circuitry. Overstimulation leads to a reduction of dopamine receptors (D2), which are necessary for erections.
Questions often arise about testosterone and heavy porn use. In some of these studies you will see that blood testosterone is not affected. Testosterone increases sexual desire by stimulating dopamine in the brain. Sexual satiety leads to fewer testosterone receptors, thus less dopamine. Sexual function doesn't correlate with blood levels of testosterone.