The health risks and benefits of the various methods of birth control vary not only according to the method used, but with the age and other characteristics of the user. For example, the Pill is the most effective and generally the safest method for teenagers. Mortality from Pill use could be reduced enormously if Pill users stopped smoking, if women did not take the Pill past age 35, and if no women took high-dose Pills. If health risks were the only consideration, a woman's safest course would be to start contraception with the Pill, continue with that method for about four years, have the number of children she desires by her mid-twenties, and then persuade her male partner to have a vasectomy. The most notable benefits of contraceptive use are some protection conferred by the Pill against ovarian and endometrial cancer, pelvic inflammatory disease, ectopic pregnancy, ovarian retention cysts, and iron deficiency anemia; considerable protection by the barrier methods, especially the condom, against sexually transmitted disease, including AIDS; and protection by male and female sterilization against ectopic pregnancy. The major disadvantages are increased risk of heart attack and stroke associated with Pill use (mainly among those over 35 who smoke); significant risk of pelvic inflammatory disease associated with IUD use; surgical complications and anesthesia deaths from sterilization and abortion procedures; and complications of pregnancy from failure of barrier methods and of periodic abstinence.