Re      : Benadryl (diphenhydramine)

Unfortunately we know very little about the breastmilk concentrations of most
of the antihistamines. I suspect that Benadryl is transferred in rather small
concentrations.  Benadryl has been used for many years for teething pain, etc,
in children and I would not necessary suggest it is definitely contraindicated
in nursing mothers.  Single doses such as for treatment of rash or allergy
would not be overly hazardous.  The only real concern about the sedating
antihistamines would be in neonates who are especially sensitive to depressant
drugs,  such as the premature, infants with apnea or breathing problems, or
weakened infants.

Tom Hale, Ph.D.