If the semen analysis shows total absence of sperms, then the diagnosis of azoospermia is logical. One of the common causes is the history of mumps. There can also be genetic causes. The prognosis in such cases is quite poor with any treatment since basically there is testicular failure.
Anti-psychotics such as risperidone can cause male sexual dysfunction such as ejaculatory disorders, loss of libido etc. but to our knowledge, no case of azoospermia (total absence of sperms) has been reported.