Nepicastat is primarily used in research settings to study its effects on the central nervous system. It acts as a selective inhibitor of dopamine beta-hydroxylase, an enzyme involved in the conversion of dopamine to norepinephrine. By inhibiting this enzyme, it helps researchers understand the role of norepinephrine in various physiological and pathological processes, such as stress, anxiety, and cardiovascular function. Additionally, it has been investigated for potential therapeutic applications in conditions like post-traumatic stress disorder (PTSD) and substance abuse, where modulation of norepinephrine levels may offer clinical benefits. Its use in these areas provides valuable insights into the development of novel treatments targeting the noradrenergic system.