Theoretically, it is possible that diphenhydramine could affect a woman's milk supply, since the medication can suppress prolactin (a hormone important for breast milk production). However, this is probably not an issue for women who are well-established with breastfeeding.
PRO is a strategic communications firm helping high profile individuals, professional teams, national governing bodies, corporations and non-profits within the sports industry build their brands through the media.
Definition of professional for English Language Learners : someone who does a job that requires special training, education, or skill : someone who is a member of a profession : someone who is paid to participate in a sport or activity