There are many possible.  Of the older ones, methyldopa is pretty good and
may even increase the mother's milk supply.

Of the calcium channel blockers, nifedipine is a good one for nursing
mothers.

Of the beta blockers, propranalol is good for nursing mothers.

Of the ACE inhibitors, captopril is fine for nursing mothers.

In fact, very few are contraindicated.  There is concern that diuretics will
dry up the milk, but I have never heard of this actually happening.  Dr.
Hale expresses concern about ACE inhibitors and there has been some concern
about atenelol, but most mothers who have used it have had no particular
problems.  However, if a beta blocker is what is wanted, there are
alternatives to atenelol.

Jack Newman, MD, FRCPC