A common method of reversible contraception is oral contraception (OC), or birth control pills (BC). The first OC pill was introduced in 1960 and contained both estrogen and progestin given in constant doses throughout the cycle. The current OC pills are modified from the original products, containing approximately one-fifth the estrogen and one-tenth the progestin found in the first pills.
Currently there are two forms of estrogenic compounds found in OC available in the United States: ethinyl estradiol and mestranol. Both of these compounds are synthetic and made to act as natural estrogen. The progestins currently available in OC include: ethynodiol diacetate, desogestrel, norgestimate, norethindrone, norethindrone acetate, norethynodrel, norgestrel, and  levonorgestrel. Each progestin differs in it's estrogenic, antiestrogenic, androgenic and progestational effect.
 

Estrogenic Effect

• Inhibits ovulation
• Secretions within the uterus are altered, altered endometrium
• Accelerates ovum transport

• Thickening of the cervical mucus hampers sperm penetration
• Slows ovum transport
• Suppression of endometrium hampers implantation
• Inhibits ovulation

1. Monophasic preparations containing 50 micrograms of estrogen.
2. Monophasic preparations containing less than 50 micrograms of estrogen.
3. Those containing less than 50 micrograms of estrogen with two sequences of progestin doses (biphasic)
4. Those containing less than 50 micrograms of estrogen with three sequences of progestin doses (triphasic).
5. Progestin pills: Oral contraceptives that contain progestin only, usually norethidrone or norgestrel ("the mini pill"), are taken daily on a continuous schedule. These products are less effective than the combination pills and are commonly associated with irregular menstrual cycles.

Combination Pills: Products that contain a combination of estrogen and progestin are the most common type. The estrogen portion suppress ovulation while  progestin prevents implantation in the endometrium and makes the cervical mucus impenetrable to sperm. These combination pills contain a constant, low dose of estrogen over 21 days plus a concomitant low, but increasing dose of progestin given over 3 successive 7-day periods (the "triphasic regimen"). The pills are taken for 21 days followed by a 7-day withdrawal period to induce menses.

Effectiveness
 The lowest first-year reported failure rate is less than 1%. Failure rate is inverse to age and is determined by the extent and type of imperfect use. Contraceptive failure has been observed in some patients taking Dilantin or antibiotics or when one or more doses are missed.

Advantages of OC's

• Decrease menstrual cramps and pain
• Prevent pain with ovulation
• Decrease number of days of bleeding and amount of blood
• Reduction of premenstrual symptoms
• Pelvic inflammatory disease protection
• Protection of ovarian and endometrial cancer
• Ectopic pregnancy prevention Improvement of acne
• No loss of fertility

• No protection against HIV/STD's
• Must be taken daily
• Missed periods, spotting, breakthrough bleeding
• Nausea and vomiting
• Mood changes
• Decreased libido

Estrogen excess
General symptoms: hay fever and allergic rhinitis, urinary tract infection.
Premenstrual symptoms: bloating, dizziness, fainting, swelling, headache (cyclic), irritability, leg cramps, nausea, vomiting, visual changes (cyclic), weight gain (cyclic)
Reproduction system: breast cystic changes, dysmenorrhea, hypermenorrhea, increase in breast size, uterine enlargement, uterine fibroid growth

Cardiovascular system: leg clots, brain clots, vascular headaches

Progestin Excess (progestins/androgens)

Progestins
General symptoms: appetite increase, depression, fatigue, tiredness, hypoglycemia symptoms, libido decrease, weight gain (noncyclic), breast regression
Cardiovascular symptoms: hypertension, leg vein swelling
Reproductive system: increased flow length, cervical inflammation
Androgens
General symptoms: acne, masculization, libido increase, oily skin and scalp, rash, swelling

Estrogen deficiency
Absence of withdrawal bleeding, early or midcycle bleeding and spotting (pill days 1-9), continuous bleeding and spotting, flow decrease, nervousness, hot flashes, vaginitis

Progestin deficiency
Late breakthrough bleeding and spotting (pill days 10 to 21), delayed withdrawal bleeding, dysmenorrhea, heavy flow and clots, hypermenorrhea
 

Comparison of Effects in Oral Contraceptives

Oral Contraceptive	Progestational effect	Estrogenic effect	Antiestrogenic effect	Androgenic effect
Norgestrel/levonorgestrel	+++	0	++	++++
Ethynodiol diacetate	++	+	+	+
Norethindrone acetate	+	+	+++	+
Norethidrone	+	+	+	+
Norethynodrel	+	+++	0	0
Norgestimate	+	0	N/A	++
Desogestrel	+++	0	+	+++

+++ = pronounced effect
++ = moderate effect
+ = slight effect
0 = no effect
N/A = information not available