There isn't any good research on atenolol.  Indeed, most women who are
on atenolol and nursing do not notice any effects on their milk or their
baby.  However, there is at least one case report of a baby developing
severe beta blockade while the mother was nursing with atenolol started
only postpartum.  The baby developed cyanosis and lethargy and had high
atenolol levels in his blood.  The pharmacology was done in Toronto Sick
Children's Hospital.  This has been written up and I am sure not to
difficult to find.  It is a convincing case report.

Because there are alternatives to atenolol, including drugs of a similar
class, such as propranalol, why use atenolol?  Nifedipine is an obvious
alternative as well, though it is in a different class of
antihypertensives.  Why not methyldopa which, as a side effect,
increases the milk supply?

I would just like to point out that we have a special approach with
drugs and breastfeeding don't we?  Many drugs which we have no
hesitation in using, have caused serious and even fatal side effects,
even when used as directed (not in overdose).  These include aspirin,
cotrimoxazole (Septra) and nifedipine.  Indeed, not to put too fine a
point on it, there is probably not one drug which has not killed or led
to the death of somebody.  But, we get one report of a side effect in a
nursing infant, and all of a sudden the drug is verboten for nursing
mothers.  We must be careful, but nobody reports cases where there are
no side effects, and for each serious side effect of amoxycillin, there
are millions of "no serious side effects". (Though mild side effects of
amoxycillin are very common).

I have never heard of atenalol causing a decrease in the milk supply,
but, of course it is possible, though I would not know how to explain
the mechanism of action.

Jack Newman, MD, FRCPC