Many different things can cause abnormal uterine bleeding. Pregnancy is a common cause. Polyps or fibroids (small and large growths) in the uterus can also cause bleeding. Rarely, a thyroid problem, infection of the cervix or cancer of the uterus can cause abnormal uterine bleeding. In most women, abnormal uterine bleeding is caused by a hormone imbalance. When hormones are the problem, doctors call the problem dysfunctional uterine bleeding, or DUB. Abnormal bleeding caused by hormone imbalance is more common in teenagers or in women who are approaching menopause.

In TCM, it is usually caused by weak constitution, insufficiency of kidney-qi, weakness of the thoroughfare and conception vessels to control menses, or excessive sexual intercourse and multiparity that impair kidney qi. Or it may be caused by spleen-deftciency in constitution, or improper diet and overstrain and excessive anxiety that impairs spleen qi and leads to collapse of qi due to deficiency. Or it may be caused by yindeficiency in constitution, or prolonged illness, hemorrhage, multiparity, excessive sexual intercourse that consumes yin-blood, deficiency of yin and water as well as internal exuberance of asthenia-fire.

It may be caused by yang-excess in constitution, or invasion of exogenous heat into blood phase, or extreme changes of seven emotions and transformation of five emotions into fire that drives blood to escape the vessels. Or it may be caused by mental depression, stagnation of liver qi, qi stagnation and blood stasis, or internal impairment due to retention of menses or lochia in the thoroughfare and conception vessels.