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Walter, Just Answer Health Expert
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Does Plan B cause missed/light periods

Resolved Question:

I am a 26 year old female with a relatively stable 30 day menstrual cycle. My last "normal" period came on June 20. On June 22, I had unprotected sex. Just to be safe I took a Plan B within 24 hrs. Subsequently, my flow got much lighter reducing to spotting, even though my period normally lasts for 5-6 days. After that I didn't have sex for about 2 weeks, when I got a urine pregnancy test done at a health center which was negative. After the test I had sex about 4-5 times, with a condom which did not leak or break. My period was supposed to come around July 20, but a few days before I started spotting again, which lasted for about 5-6 days. I'm still waiting for my normal period, 7 days after it was due. I have been doing home pregnancy tests over the last week which are negative and again went to the health center to get a urine test done which was negative. Is Plan B causing the light "period"? Was it a period? When will I know for sure that I'm not pregnant?
Submitted: 9 years ago.
Category: Health
Expert:  Walter replied 9 years ago.


There are numerous reasons why your menstruation cycle can run late, Pregnancy and stress being the most common. The light periods can be from the Plan B or from early pregnancy.

Since you keep getting negative results, make sure you repeat the test in two weeks to make sure. You also should consider whether or not you've recently been sick, gained or lost a significant amount of weight, have been under excessive stress or have taken any new medications. All of these things can affect your menstrual cycle and cause you to have irregular periods.

I would bring it up at your next doctors appointment, if you continue to miss cycles it is a good idea to set up an appointment with your doctor to determine the cause and begin any needed treatments.


Customer: replied 9 years ago.
Reply to Walter's Post: I haven't had any of the conditions that you mentioned, that is, stress etc. and I've never had irregular periods before. From whatever research I could do, I found out that pregnancy tests should be fairly accurate about a week after your missed period(which is true in my case). My question is when will I know at the earliest for sure that I'm not pregnant? Is repeating a test two weeks from now going to be more conclusive? Another question I have is whether women who have used Plan B have had similar problems? I know of light periods, but are they light to the extent of just spotting?

Thanks very much!
Expert:  Walter replied 9 years ago.


While some women do get accurate results within a week this is not the case all the time and many many women are unable to get a accurate result until they are at least two weeks late.

Yes many women experience late r spotty periods after taking the plan B while it is not a common thing it can occur.


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