This is a common thought, but it’s actually not true!
Many women who are worried about low milk supply have heard that drinking beer can help. However, this is actually a myth, and in fact it can be harmful! Consuming alcohol has actually been shown to lead to decreased milk supply, as well as delayed milk let down. This idea that beer helps probably stems from the fact that barley — which is found in beer — has been shown to give some women a boost in milk production.
If you are worried about your supply, skip the beer for this purpose (though drinking an occasional one during breastfeeding is perfectly fine), and talk with your doctor or lactation consultant about other ways to manage your production.