Propranolol, a beta blocker, is known to have the potential for causing sexual side effects, such as impotence and Peyronie's disease. While uncommon, sexual side effects are thought to be a class effect, meaning it is associated with all beta blocker medications.


Propranolol's effect on fertility is currently unknown however. One study, conducted with mice, showed that propranolol administration caused a decrease in sperm motility, an increase in sperm abnormalities and a slight reduction in testosterone levels. Humans have not been studied in this regard however.


There haven't been any studies looking at fertility rates in humans taking propranolol, but there are studies that theorize that propranolol could affect fertility due to the drug being present in the seminal fluid and the apparent ability of propranolol to inhibit sperm movement activity. 


In fact, propranolol has been studied in the past as a possible contraceptive, with intravaginal administration resulting in spermicidal activity. It is unknown however, if the concentration of propranolol present in the seminal fluid would be high enough for such effects.


So, while most sources don't list infertility as a possible side effect of propranolol, it could theoretically be possible due to the known effects of propranolol on sperm and the fact that the drug is present in the seminal fluid. Nothing is conclusive however.