Medically reviewed by Carolyn Kay, M.D.
Updated on February 10, 2023
Plan B works to prevent pregnancy by delaying ovulation. If you have sex without adequate contraception during ovulation, other options, like the copper intrauterine device (IUD), may be more effective in preventing pregnancy.
It’s pretty simple: No morning-after pill works during ovulation, as they’re designed to delay it. If ovulation is already happening, Plan B (or any other emergency contraceptive pill) will have failed before it’s even begun. But knowing whether you’re ovulating can be tricky.
If there is a risk that Plan B fails, the copper intrauterine device (IUD) is your best bet. Not only is it a highly effective emergency contraceptive, but it can also be used for long-term contraception.
The best way of preventing pregnancy throughout your cycle is to use a long-acting form of contraception.
There are several methods to choose from, including:
Barrier methods, such as condoms, are also an option. However, these methods are less effective than the above. Of course, you’d need to be using these before you have sex.
If you have sex without adequate contraception during ovulation, the copper IUD (ParaGard) is the safest emergency contraceptive trusted source. You’ll need to have it inserted within five days after sex or ovulation for it to work. Once in, the copper makes it difficult for sperm to reach the egg, reducing the chance of pregnancy by more than 99 percent. Plus, you can keep it in for use as a regular contraceptive for up to 10 years.
Taking a morning-after pill during ovulation won’t harm your body. But you may still become pregnant. That’s because pills, like Plan B, can *delay* ovulation to prevent pregnancy. But if you’re already ovulating, an egg has already been released. And sperm — which can live in your body for up to 6 days — is more likely to reach it. If you’re not sure where you are in your cycle and the morning-after pill is your only option, taking it may be worthwhile. After all, you might have not ovulated yet, and it could make a difference.
Worth mentioning: Some morning-after pills are less effective for people who weigh more than 155 pounds, so keep that in mind as you decide which emergency contraceptive option is best for you.
If you’re able to, reach out to a doctor or other healthcare professional for help. Your local clinic or Planned Parenthood may be able to offer advice and provide you with the pill.
It’s a tough one. There are some physical signs to look out for.
For example, more or clearer vaginal discharge can be a sign that you’re ovulating. You may also experience tender breasts and bloating. Hormone levels also rise at this time — you can measure this with a kit that you urinate on. Some people even use fertility or menstrual tracking apps to help them predict ovulation.
Although ovulation tends to happen between 10 and 16 days before your period, the exact day can change from month to month.
Plan B’s manufacturers say the morning-after pill may prevent fertilization if ovulation has already happened.
It all depends on when your period is due. If you consistently track your menstrual cycle and know exactly when your period should arrive, only take a test if it’s at least a week late.
Unfortunately, periods aren’t always the most predictable of things. So, if you’re unsure when it’s due, you may need to wait a little longer. That’s because pregnancy tests work by detecting levels of human chorionic gonadotropin (HCG), a hormone that doesn’t show up straight away.
If you didn’t take a morning-after pill, take a test 2 weeks after sex. You can always take another test two weeks after the first one to double-check the result.