It is known that some cancers need sex hormones to thrive, which is why an increased risk of breast cancer has been linked to elevated estrogen levels in women. The National Cancer Institute states that some studies have shown an increased risk of breast cancer in women taking oral contraceptives, while other studies have shown no change in risk. Generally, women older than 45 years of age who have been taking birth control pills for most of their adult lives have the highest risk of breast cancer for two reasons: long-term consecutive use of the oral contraceptive and use of earlier versions that had higher levels of sex hormones.
The National Cancer Institute also notes that oral contraceptive use has been shown to increase the risk of cervical cancer and liver cancer. On the other hand, multiple studies indicate a potential decrease in risk of ovarian and endometrial cancers for women on oral contraceptives.
Other Long-Term Side Effects
Other long-term side effects from oral contraceptive use include an increased risk of blood clots, heart attack, stroke, weight gain, hypertension and migraine headaches. These effects seem to be increased by cigarette smoking. Long-term use of synthetic hormones has also been linked to nutritional deficiencies, such as low levels of vitamins B2, B6 and B12, depression and increased feelings of anxiety, according to "Hormone Replacement Therapy and The Brain."