How do contraceptives affect periods?

Hormonal contraceptives use either progestin or estrogen, or both, to stop a pregnancy from occurring, and these hormones are also important in the menstrual cycle. It makes sense then that hormonal contraceptives will affect your periods.
Depending on the type of contraceptive that you use, it can cause lighter or heavier bleeding and can also influence the length of your period. Also, bleeding patterns tend to change as time goes on.