10 most common birth control pill side effects The oral contraceptive pill, commonly known as "the pill, " is a hormone-based method of preventing pregnancy. It can also help resolve irregular menstruation, painful or heavy periods, endometriosis, acne, and premenstrual syndrome (PMS). Birth control pills work by preventing ovulation. No egg is produced, so there is nothing for the sperm to fertilize. Pregnancy cannot occur. "The pill" is used by nearly 16 percent of women aged 15 to 44 years in the United States, and it has both advantages and disadvantages. People with different risk factors may be advised to use a particular kind of pill. There are different types of contraceptive pills. They all contain synthetic forms of the hormones estrogen, progesterone, or both. Synthetic progesterone is called progestin. Combination pills contain progestin and estrogen. The "mini pill, " contains only progestin. Monophasic pills all contain the same balance of hormones. With phasic pills, two or three different types of pill are taken each month, each with a different balance of hormones. Another option is "everyday pills" and "21-day pills." A pack of everyday pills lasts 28 days, but seven of the pills are inactive. The everyday pill may be easier to use correctly, as the routine is the same every day. Used correctly, the pill is highly effective, but because people make mistakes, 6 to 12 pregnancies in every 100 are thought to occur each year while using it. The Centers for Disease Control and Prevention (CDC) put the failure rate for both types of pill at 9 percent. Birth control pills do not prevent sexually transmitted diseases (STDs). Only a condom can help prevent this type of infection. Side effects Common side effects of oral contraceptives include: birth control pill packets Hormonal contraception is taken to prevent pregnancy and for other medical reasons. intermenstrual spotting nausea breast tenderness headaches and migraine weight gain mood changes missed periods decreased libido vaginal discharge changes to eyesight for those using contact lenses We will look at each of these side effects in detail below.