Birth Control Pills and Menstrual Cramps

This is an unusual complaint for someone taking the birth control pill. Most of the time, BCPs make menstrual cramps better, not worse. For many women, their menstrual cramps disappear altogether.

There are two reasons for this usual improvement in cramps, and both are related to the strength of the progestin half of the birth control pill. Progestin normally suppresses ovarian function, inhibiting ovulation and also markedly reducing estrogen levels. The other half of the birth control (the estrogen half), builds the woman's estrogen levels back up, but usually to a level that is lower than what they started out with.

These generally lower levels of estrogen mean that the lining of the uterus (endometrium) has less buildup at the time of the menstrual flow, leading to lighter, shorter periods. This in turn provokes fewer menstrual cramps.

The other hormonal impact of the progestin half of the birth control pill is to block uterine contractions. Progestins have smooth muscle relaxing properties, and the uterus, itself a large smooth muscle, will relax in the presence of progestin. This leads to reduced or eliminated menstrual cramps.

But both of these impacts are more dramatic with stronger progestins with long half lives. The weaker progestins, or those that wear off quickly, may not suppress ovarian function very well, and may be more inconsistent in their suppresion of uterine contractions. They will still prevent pregnancy, as the BCPs do many other things that are contraceptive in nature, but they may not prevent cramps, and often the cramps worsen if ovarian function is not inhibited.

Understanding the physiology of the interaction between BCPs and menstrual cramps will lead to a number of possible clinical responses to resolve the issue.

1. Most of the time, these increased cramps are because the BCP is not strong enough to consistently suppress ovarian function. Changing to a stronger progestin with a longer half life (such as levonorgestrel) will frequently resolve the problem, particularly if attention is paid to taking every pill, on schedule. In a few cases, taking the pill continuously may be necessary to achieve this goal.
2. In a minority of cases, worsening menstrual cramps will be due to the new onset of a medical or gynecologic problem, such as endometriosis or PID. A pelvic examination can usually determine the presence of these conditions as both will demonstrate pelvic tenderness, while menstrual cramps have tenderness only while the cramping is present.