Women taking Letrozole, it is possible to cause vaginal bleeding, or bleeding symptoms caused by other factors. 1. Adverse reaction: Letrozole is a kind of breast cancer treatment drug, is a kind of aromatase inhibitor, can inhibit aromatase to promote the decline of estrogen level, help to eliminate the stimulation effect of estrogen on the growth of tumors, one of the adverse reactions of this drug is to cause vaginal bleeding. 2. Other factors: there are many factors that cause vaginal bleeding, such as women do not pay attention to local hygiene, resulting in bacterial infection, induced gynecological diseases, may also cause vaginal bleeding. Normal menstruation in women can also cause vaginal bleeding. Adverse effects of Letrozole generally include fatigue, nausea, hot flashes, and arthralgia, etc. It is contraindicated for those who are allergic to Letrozole. Letrozole carries some risks and patients need to be supervised by a specialist.