There are two main types of oral contraceptive birth control pills (OCPs): pills containing a combination of ethinyl estradiol (EE, a synthetic form of estrogen) and progestin (a synthetic form of progesterone), and pills containing only progestin. The method of action is different between the two types of OCPs. The contraceptive effect of combination pills is mainly due to estradiol blocking the release (ovulation) of an egg every month. Progesterone only pills work primarily by making the cervical mucous inhospitable to sperm and the uterine lining inhospitable to the embryo. Progestin-only pills are prescribed mainly for women who shouldn't be exposed to elevated estrogen levels.
Types of Combination Birth Control Pills
Within the category of combination OCPs, there are two subtypes, monophasic (same EE/progestin dose) and multiphasic, (varying EE or progestin dose) in the active pills. The traditional monophasic combination pills have active pills containing the same EE/progestin dose in every pill, taken for 21 days, followed by a week of placebo pills which allow a period to occur when hormone levels drop. Multiphasic OCPs have varying doses of either EE or progestin in the active pills to more closely mimic the natural alterations in estrogen and progesterone in the menstrual cycle. Multiphasic pills were developed in an attempt to minimize side effects from traditional monophasic combination OCPs.
Monophasic OCPs
The levels of EE in monophasic pills have steadily dropped since the first birth control pill (Enovid-10), which had 150mcg EE. Modern formulations have between 20mcg and 50mcg EE, a range that's closer to natural levels than the original formulation. Depending on the brand, the amount of progestin used is usually between 0.4mg and 1mg. Monophasic type pills have the same mix of estradiol and progestin in each active pill. For example, Orthum Novum 1/35 has 35mcg EE and 0.4mg progestin in each active pill taken over 21 days, followed by one week of placebo pills.
Multiphasic OCPs With Changing Progestin Dose
Multiphasic type pills have 21 active pills with one hormone (for example, EE) at a constant dose and the other hormone (progestin) with a changing dose over the 21 days. For example, Orthum Novum 7/7/7 has 35mcg EE in every pill, with 1mg progestin in the pills taken the first seven days, followed by 0.5mg progestin for the next seven days and 1mg progestin for the final seven active pill days. The purpose of lowering the overall progesterone dose is to decrease side effects in women who are more sensitive to progesterone.
Multiphasic OCPs With Changing Estrostep Dose
To decrease EE-related side effects such as breakthrough bleeding in the early days of the cycle, an OCP with a steady progestin level and varying EE may be beneficial. Estrostep with iron is an example of this type of multiphasic. Estrostep OCPs contain 20mcg EE for five days, 30mcg EE for seven days, nine days of 35mcg EE, followed by placebo pills.
Progestin-only OCPs
Progestin-only OCPs were developed for women who can't take EE due to an existing cardiovascular disease, which can be worsened by taking EE. Other conditions preventing women from taking EE containing OCPs are a history of stroke, blood clots in veins, lupus, cigarette smoking in women older than 35 years, breast feeding and a history of migraine headaches from OCPs containing EE. The most common side effect from progestin-only OCPs is breakthrough bleeding because there is no EE to support the uterine lining and prevent bleeding.
Customize Your OCP
Depending on your specific risk factors and needs, your physician can prescribe a type of OCP for you that prevents pregnancy with minimal side effects. Some women are more sensitive to side effects from either EE or progestin. Side effects can be minimized by altering hormone levels of EE, progestin or both. Your physician should be able to help you customize your OCP to your needs. If one formulation isn't right for you, there are dozens of other formulations to try.
References
- Book:"Contemporary Guide to Contraception",Steven T. Nakajima, MD,2007
