The Progesterone-Only Pill: What to Expect

The progesterone-only pill (POCP or ‘mini-pill’) is an oral contraceptive that can be used by women who aren’t able to use the usual combined progesterone and estrogen pill due to headaches, high blood pressure, blood clots or other conditions.

The main ‘drawback’ of progesterone in this form is that it needs to be taken at the same time (or roughly the same time) every day in order to be effective. Otherwise, it is similar to the combined pill and is generally a safe and effective form of contraception.

Basics of the Progesterone-Only Pill

When taken regularly, the progesterone-only pill is effective more than 99% of the time. This means that fewer than one out of a hundred women will get pregnant when using it each year.

The basic mechanism of action for the progesterone-only pill is that it thickens the mucus in the cervix and thus prevents the sperm from reaching the egg. POCPs can also affect the ovaries to some extent and in some cases may stop ovulation entirely (generally with newer pills).

Essentially, progesterone is a hormone that regulates the amount of estrogen in the body. Progesterone belongs to a category of steroid hormones called progestogens. It is secreted by the corpus luteum in the ovary during the latter half of the menstrual cycle and is heavily involved in maintaining the stages of pregnancy.

Potential Side Effects

Progesterone is considered safe when taken orally and levels change in the body naturally during pregnancy. However, it can cause a few potential side effects and have a few unexpected side effects on the body. For instance:

  • Progesterone can cause acne or help it clear up
  • Progesterone can interfere with your menstrual cycle, causing light or infrequent periods or stopping them altogether
  • Breasts may get larger or smaller and may become sensitive
  • Progesterone can either increase or decrease libido
  • Other side effects including headaches, increased risk of illness, mood swings and more may also occur but are uncommon

One very concerning potential side effect of POCP, is the increased risk of breast cancer. However, in extensive studies there has been no conclusive evidence that this is in fact a problem (1) and certainly not more-so than for the combined pill (2).

While some ill-effects can occur as a result of progesterone use, they are generally not expected and in fact progesterone can be therapeutic for treating most of the same conditions in some circumstances.

Taking Progesterone

As mentioned, progesterone needs to be taken at the same time every day but usually there is a window of three or twelve hours during which any variation is fine. Progesterone-only pills such as desogestrel and cerazette are ’12 hour pills’ meaning that you can take them any time as long as it is within 12 hours of your last dose. Otherwise, try to remain within a three hour window when using them.

The only repercussion of missing your pill is that it will not be as effective for that day, increasing your risk of pregnancy. You should then take your pill as soon as you remember and from then on return to your normal regime.

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