Currently, there are three types of oral contraceptive pills: combined estrogen-progesterone, progesterone only and the continuous or extended use pill.  The birth control pill is the most commonly prescribed form of contraception in the US.  Approximately 25% of women age 15-44 who currently use contraception reported using the pill as their method of choice.  The most commonly prescribed pill is the combined hormonal pill with estrogen and progesterone.  Progesterone is the hormone that prevents pregnancy, and the estrogen component will control menstrual bleeding. [1] Birth control pills are primarily used to prevent pregnancy.  The effectiveness of this form of birth control is referred to as typical and perfect use.  Typical use, meaning the method may not always be used consistently or correctly, results in a failure rate of 9 women out of 100 that will become pregnant during the first year of using this method.  Perfect use, meaning the method is used consistently and correctly every time, is less than one woman out of 100 will become pregnant in the first year of use.  Due to human error, the quoted failure rate for combined oral contraceptive pills is the typical use of 9%.  OCP’s can be used to address other health conditions particularly menstrual related disorders such as menstrual pain, irregular menstruation, fibroids, endometriosis-related pain and menstrual- related migraines.[2]  Use of combined pills for acne has been formally approved by the FDA for specific brands.  The majority of women take OCP’s to prevent pregnancy, but 14% used them for non-contraceptive reasons.

The progesterone is primarily responsible for preventing pregnancy.  The main mechanism of action is the prevention of ovulation; they inhibit follicular development and prevent ovulation. [1] Progestogen negative feedback works at the hypothalamus to decreases the pulse frequency of gonadotropin releasing hormone.  This, in turn, will decrease the secretion of follicle- stimulating hormone (FSH) and decreases the secretion of luteinizing hormone (LH).  If the follicle isn’t developing, then there is no increase in the estradiol levels (the follicle makes estradiol).  The progestogen negative feedback and lack of estrogen positive feedback on LH secretion stop the mid-cycle LH surge.  With no follicle developed and no LH surge to release the follicle, there is the prevention of ovulation.  Estrogen has some effect with inhibiting follicular development because of its negative feedback on the anterior pituitary with slows FSH secretion; it’s just not as prominent as the progesterone’s effect.  Another primary mechanism of action is progesterone’s ability to inhibit sperm from penetrating through the cervix and upper genital tract by making the cervical mucous unfriendly.[1]  Progesterone induced endometrial atrophy should deter implantation, but there is no proof that this occurs. 

Combined oral contraceptive pills are to be taken daily at approximately the same time each day.  Avoid taking them greater than 24 hours apart as this could affect efficacy.  When you initiate the contraceptive pills you are not protected from pregnancy prevention in the first 7 days and an alternative method of birth control is recommended during this time period.  If you miss a tablet just take the missed tablet as soon as you remember and the next tablet at the usual time (taking 2 tablets in 1 day).  If you miss 2 tablets in a row in the first or second week then take 2 tablets the day you remember and 2 tablets the next day, then resume 1 per day.  Use another form of contraception until you begin a new cycle.   The extended cycle formulations have active hormone pills for every day for 3 months, followed by a week of placebo.  This can be manipulated and are formulations that involve taking active pill for 1 year which will functionally stop all menstrual bleeding; although the most common complication from extended cycle is break through bleeding.  Any formulation of combined oral contraceptive pill can be used in this manner but typically the monophasic pills the easiest to manipulate.  

Most side effects of OCP’s are mild and disappear with continued use or switching to another pill formulation.  The most common adverse effect of combined oral contraceptive pills is break through bleeding.  Women will also complain of nausea, headaches, abdominal cramping, breast tenderness, and an increase in vaginal discharge or decreased libido.  Nausea can be avoided by taking the medication at night before sleep.  The majority of the other consequences will resolve with time or switching OCP to a different preparation.  

There are a few absolute and relative contraindications of oral contraceptive use.   Women with uncontrolled hypertension should not initiate oral contraceptive use until their hypertension is being managed; diabetics may experience some hyperglycemia when initiating OC’s but these are issues that can be addressed.  However OCP’s are contraindicated in smokers over age 35 due to significant risk for cardiovascular events and specifically deep vein thromboembolism. Risk of venous thromboembolism is increased among OC users 3-9/ 10,000 woman-years compared with nonusers who are not pregnant and not taking hormones (1-5/10,000 woman-years), the risk is even greater in those over 35 and smoking.[3] Women with a history of VTE, known ischemic heart disease, migraines with auras, active or history of breast or endometrial cancer and valvular heart disease should not use OC’s as these conditions represent unacceptable health risks.  There are too many available alternatives for the patient to prevent pregnancy and not increase the patients’ health risk.