University of Michigan:
"If you have gallstones and are taking birth control pills, you may want to ask your health care provider if you should use another method of birth control. "
And, according to the National Digestive Diseases Information Clearinghouse (NDDIC):
"Women are twice as likely as men to develop gallstones. Excess estrogen from pregnancy, hormone replacement therapy, and birth control pills appears to increase cholesterol levels in bile and decrease gallbladder movement, which can lead to gallstones."
Gallstones can cause anything from annoying discomfort to life-threatening illness.
One more item to add to our list of many reasons to consider Natural Family Planning and avoid synthetic hormones.