Cutting by a third might not be an option because they might not make pills in the right dosage.

I think you could consult the PDR (Physician's Desk Reference) to find out what dosages are available. Most libraries would have it, or you could check their web site: PDR.net. Warning: the language could be very technical—it's designed for physicians, not laymen. If you're not already familiar with the PDR, read the article at Wikipedia.