Final answer:
The combined oral contraceptive pill, which contains estrogen and progesterone, decreases the risk of endometrial and ovarian cancer, as well as PID, endometriosis, benign breast changes, and ectopic pregnancy, while providing effective contraception.
Step-by-step explanation:
The contraception that decreases the risk of both endometrial and ovarian cancer, as well as the risk of Pelvic Inflammatory Disease (PID), endometriosis, benign breast changes, and ectopic pregnancy, is the combined oral contraceptive pill, commonly known as the birth control pill. The pill contains both estrogen and progesterone, which prevents ovulation, thickens cervical mucus, and changes the uterine lining, making it less receptive to implantation. The use of hormonal methods such as birth control pills is associated with a reduced risk of several reproductive system conditions and provides effective contraception, with a very low failure rate with perfect use. It is important to note, however, that there are some potential side effects with oral contraceptives, including an increased risk of blood clots and a slight increase in the risk of breast cancer, though these risks are considered less than the health risks associated with pregnancy.