In studies, there have been no clear conclusions to birth control's affect on body temperature.

What Is Basal Body Temperature?

It's important to first understand how a woman's Basal Body Temperature (BBT), the lowers normal threshold level during times of rest, can fluctuate when not on birth control. Right before monthly ovulation, a woman's BBT drops a fraction, but not for long. Within 12 hours of that point, it starts to rise back up a few tenths of a degree and remains there until the beginning of the next menstrual cycle. Woman using the BBT birth control method keep track of the first three days of their body's elevated temperature, as it corresponds to the fertile time of the month.

Birth Control Does Cause BBT Fluctuations

Since birth control pills are designed to suppress the fertile period of a woman's monthly cycle and the overall cyclical process of ovulation, they should theoretically help a woman maintain a body temperature throughout that is closer to the BBT. However, because they contain the hormone progesterone, the actually can similarly raise the BBT a fraction. Some of the best research showing that progesterone in birth control pills can raise the BBT of a woman comes from similar research of in-vitro fertilization patients. One study of 87 women found that there was indeed a link between the two, but could not determine the specific nature of how the fluctuations were caused.

Progesterone and Estrogen Battle It Out

The lack of clear research conclusions has been further compounded by the effects the two main hormones in birth control pills - progesterone and estrogen - have on each other. One recently concluded again that the mechanism(s) by which these two powerful agents affect the regulated BBT of a woman have not been immutably established. So the answer to this question is that we still don't quite know if and how birth control pills affect body temperature.