Does daylight saving time affect birth control pills?

Every fall, we “fall back” with the end of daylight saving time by moving our clocks back one hour. And every spring, we “spring forward” with the start of daylight saving time by moving our clocks forward one hour.

The goal of daylight saving time is to give us an extra hour of sunlight at the end of the day during the spring and summer. But once daylight saving time ends, the goal is to give us an extra hour of daylight in the mornings during fall and winter. 

It often takes our bodies a few days to adjust to this new schedule, and usually there are no major issues. But here are some questions my patients often ask me about daylight saving time and birth control:

Should you change the time you take your birth control pills when daylight saving time begins or ends?

Most oral contraceptive pills maintain their full effect for at least 24 hours, and changing the timing by one hour one way or another won't make a difference in effectiveness. 

The most important reason to take the pill at the same time every day is to make it part of your routine and not skip any days. So if you’re used to taking it at 10 p.m. every day, you should continue to do so whether it is 10 p.m. standard time or 10 p.m. daylight saving time.

Does taking a birth control pill an hour later or earlier make it less effective?

As mentioned above, a one-hour time shift in taking birth control pills usually isn’t a problem.

One possible exception is the progesterone-only pill, sometimes referred to as a “mini-pill.” This is a very low dose of medication, with a peak effectiveness about six hours after ingestion, but it does start to wear off beyond 24 hours.

Women who use this method exclusively should try to take the medication at the same time every day, but before the time of day they’re likely to have sex. If this pill is taken more than three hours late, a back-up form of contraception should be used.

Expert Guide to a Healthy Pregnancy: Answers to more of your questions

If you want to change the time you take your birth control pill, what’s a safe way to do this?

Generally speaking, it’s better to be early taking your pill than late in terms of preventing pregnancy. So if you usually take your pill at night, but then decide to start taking it in the morning, starting the next day is OK — even if it's been less than 24 hours.

If you usually takes your pill in the morning and want to start taking it at night, waiting until the following evening is still OK (provided that you then take the pill regularly after that). However, if it’s in the first week of the new pack, you should probably use a backup form of birth control for that week just to be safe.