Birth control pill formulations


Birth control pills come in a variety of formulations. The main division is between combined oral contraceptive pills, containing both estrogens and synthetic progestogens, and progestogen only pills. Combined oral contraceptive pills also come in varying types, including varying doses of estrogen, and whether the dose of estrogen or progestogen changes from week to week.

Mechanism of action

Combination pills usually work by preventing the ovaries from releasing eggs. They also thicken the cervical mucus, which keeps sperm from penetrating into the uterus and joining with an egg. The hormones in combination and progestogen-only pills also thin the lining of the uterus. This could prevent pregnancy by interfering with implantation of a blastocyst.
Main action in typical use is prevention of ovulation.

Combined oral contraceptive pills

All contain an estrogen, ethinylestradiol or mestranol, in varying amounts, and one of a number of different progestogens.. They are usually taken for 21 days with then a seven-day gap during which a withdrawal bleed occurs. These differ in the amount of estrogen given, and whether they are monophasic or multiphasic. The introduction of extended-cycle monophasic pills has shown that the withdrawal bleeding intervals can be decreased.

Monophasic

These are typically given as 21 tablets of estrogen and progestogen, followed by seven tablets of placebo or an iron supplement, although some newer formulations contain more active tablets and fewer placebos. Everyday regimens, which include seven inactive placebo pills, are rarely used in UK practice. Different formulations contain different amounts of estrogen and progestogen:
s use a progestogen alone with doses taken continuously and no or a short gap between packs taken. People who use them may experience irregular light bleeds, and whilst irregular in the first few months of taking, usually settles to a regular pattern in time.
The following progestogens are used:
Generally oral contraceptives should not be used in people who currently have the following conditions:
More comprehensive guidelines that include analysis of risks and benefits can be found in the World Health Organization Medical Eligibility for Contraceptive Use Guidelines which are reflected in the CDC Medical Eligibility for Contraceptive Use Guidelines.