In 1989, there was a study that showed the important role of relaxation in milk production -- mothers whose babies were in the NICU listened to a relaxation tape each day, and after a week it was found that
Since the study only included mothers with babies in the NICU, it's hard to know if the results can be generalized to different circumstances, older babies, etc, but it's a method that it couldn't possibly hurt to try!Moms in the relaxation tape group made an average of 90.1 ccs (about 3 ounces) – compared with only 55.4 ccs in the control group, for an average difference in milk production of 63%. Feher and his colleagues found that the tape was even more effective among mothers of babies who were so sick that they were on a mechanical ventilator – mothers who were asked to listen to the relaxation tape made 121% more milk than those who were not. They also found that the more frequently a mother listened to the tape, the more milk she was able to make.
There's more information at the Breastfeeding Medicine blog, along with a podcast of the relaxation recording.