Types of Oral Contraceptives

A. Combination (estrogen/progestin) OCs

Combination OCs contain both estrogen and progestin, and are classified as either monophasic, triphasic, or biphasic. Synthetic rather than natural hormones are used in OCs because their greater potency allows for more predictable results. The two estrogens used in OCs are ethinyl estradiol and mestranol (see Table 1 below). In the body, mestranol breaks down to ethinyl estradiol.

Progestins used in OCs are synthetic progesterones, or in other words, produced in laboratories. Seven different progestins are used in OC formulations (see Table 1 below). Different progestins have different strengths and side effects. They were developed to give physicians more choices for each woman to see which OC is tolerated best.

Most combination OCs are given as active pills for 21 days followed by a 7-day hormone-free period to allow for withdrawal bleeding. Some packets of combination OCs contain only 21 pills all of which are active. Others also include seven placebos, hormone-free pills in another color. Many users prefer the 28-day packets since they do not need to make a calendar notation as to when to begin their next cycle of pills. One brand of pills contains estrogen-only pills in the fourth week.

The amount of estrogen and progestin in individual pills, of a combination OC packet may vary depending on when in the cycle the pill is taken.

• Monophasic OCs contain the same dosage of each hormone in each active pill.
• Biphasic OCs alter the progestin/estrogen ratio in 2 phases.
• Triphasic OCs alter the progestin/estrogen ratio in three multi-day phases by varying the amounts of progestin, estrogen, or both.

Biphasic and triphasic OCs are thought to approximate a woman's natural hormonal fluctuations more closely by varying the progestin/estrogen ratios. The aim of these formulations is to minimize the occurence of breakthrough bleeding and amenorrhea while maintaining efficacy. However, some physicians and patients prefer monophasic OCs because they are less confusing (all active pills are the same color and have the same dose of hormones).

C. Progestin-Only OCs

Also called minipills, progestin-only pills (POPs) are indicated for women who should not take estrogen containing pills. These include women who are breastfeeding, who are hypertensive, or who are at risk for developing blood clots. Minipills are estrogen-free oral contraceptive tablets that provide a continuous flow of low dose progestin. Unlike combination OCs, progestin-only pills must be taken continuously without a hormone-free period. Minipills are slightly less effective than regular pills and often cause irregular menstrual patterns. Minipills prevent pregnancies mainly by making the cervical mucus impermeable to sperm and by making it more difficult for an egg to attach to the uterus lining.

D. Effects of Different OCs

There are many different OC brands. In some cases, different brands are identical except for packaging. In other cases, brands have different hormones in slightly differing amounts. When prescribing a pill, physicians may consider estrogen dose, progestin dose,type of progestin and relative potency as important factors. The risk of serious side effects is higher among women who take more than 50 mcg of estrogen. Most physicians now recommend that women take pills containing 35 mcg or less. Thus, the ideal pill is the one with the lowest estrogen and progestin doses that will be effective in preventing pregnancy and minimize adverse effects.