Does ejaculation affect testosterone?

Ejaculation does not reduce testosterone levels. However, it does lead to an increase in prolactin levels, which affects the male refractory period during which sexual activity cannot occur again 1. Moreover, sexual behavior, including the act of sex itself, can increase testosterone levels. Abstinence or avoiding ejaculation for a week or more can lead to even further increases in testosterone, up to 400% 1.

Thus, while sex itself tends to raise testosterone, abstaining from ejaculation can have an even greater effect on increasing these levels.