Will Plan B Cause You To Miss Your Period?

In our latest question and answer, our pharmacist discusses how emergency contraception such as Plan B can affect your menstrual cycle.

Dec 01, 2017

Anon223 asked

Hi, I took the morning after pill the first week of November and had a 3/4 day period ending on the 9th November. I then stupidly took it again a week later and since then have had spotting but no period. I did a pregnancy test but it’s came up negative. Have I just not got my period as I’ve taken 2 pills and its messed up my cycle or something else??

Answer

Emergency contraceptives, such as Plan B, contain a large dose of the progestin hormone, levonorgestrel. It is thought to prevent pregnancy after unprotected sex by either inhibiting or delaying ovulation. It may also impact egg fertilization and implantation.

The use of oral emergency contraception (e.g. Plan B) is well known to cause significant, but short lived, changes to the menstrual cycle as you are ingesting a large hormonal dose. In fact, all of the following have been reported and are possible after taking Plan B:

  • Change in menstrual cycle length (shorter or longer)
  • Change in the menstrual appearance (lighten or darker than usual)
  • Change in intermenstrual bleeding frequency (e.g. 'spotting)

In studies evaluating how emergency contraception affects the menstrual cycle, it appears that taking it earlier in the menstrual cycle is associated with a shortened cycle and increased spotting. Taking it later in the menstrual cycle tended to prolong or result in the absence of the menstrual cycle.

There is not much data available in regard to how two full doses of emergency contraception may affect you menstrual cycle, but we can certainly infer that the adverse reactions may be more significant versus taking one dose. This could certainly include spotting and amenorrhea (absence of a menstrual cycle). The closer to menses you take hormones, the likelier it is to 'miss' your period.

It is extremely important to take a pregnancy test to rule out pregnancy as the reason for not having your period. It is recommended that you reach out to your doctor so they can take a more conclusive test to confirm you are not pregnant.

Lastly, data suggests that your menstrual cycle will should begin to return to normal one full cycle after taking the emergency contraception. If you continue to experience unusual spotting or bleeding, please contact your doctor.

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