You may feel like you have more milk at first after drinking a beer. In the long run alcohol dries you out.
Alcohol disrupts the hormones that are involved in milk production.
Julie Mennella, a researcher at the Monell Chemical Senses Center in Philadelphia who studies alcohol's affect on lactation, explains that while prolactin (a hormone that aids milk production) increases with alcohol consumption, oxytocin (a hormone that's responsible for milk letdown) decreases. Researchers think this may explain why babies have a harder time breastfeeding when their mothers drink alcohol.