While a few substances can affect milk volume, the single most important factor in milk supply is regular removal of milk. Hormonal contraceptives may cause a sudden and possibly permanent drop in milk supply. Even progesterone-only products may affect some women. Be cautious of using these drugs. Maintaining a milk supply usually becomes easier and more reliable over time.
Some mothers can extend the time between pumpings.
Others find that their breasts release milk faster over time and therefore can shorten the time of the pumping session. Please read about the Lactation Amenorrhea Method of fertility awareness. Maintaining a milk supply for a baby is a separate issue from how the milk is fed to the baby and the mother-baby relationship. Pay as much or more attention to the baby as the pump. Please call a lactation consultant if you think your supply is dropping.