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When does Depo Provera become effective if not taken during your period?

I used to take depo provera when I was younger, but i'm pretty sure I had gotten it during my period the first time. Its been a few years since ive had it and I already had my period when i was finally able to make it in to get it this time around and was only able to see the nurse who gave it to me. No information was given to me about when it becomes effective if you get it after your period, so i looked online and most things say you need to wait 7 days after you get it if you werent on your period. However when I called my doctors office now that they are open and asked them and informed them i was not on my period when i got the shot a few days ago, they are telling me it is effective immediately.
This is an important question to discuss with your OB/GYN. I think that in some sense, both answers are correct, but for practical purposes, in general I would go with the 7 day rule. The Depo Provera shot prevents pregnancy in two ways. First, it puts your cervix in a post-ovulation state which is closed with a type of mucous production that is not friendly to sperm. This effect should happen fairly quickly I would say within a day of the shot. However, this effect is not the only way it prevents pregnancy. The shot also prevents ovulation which is probably the more important reason why it prevents pregnancy. While it probably prevents ovulation within a couple of days of the shot, an ovulated egg (for example on the day you get the shot) could live in the fallopian tube for 1-3 days. Thus, you could still get pregnant during that time period. The 7 day rule is chosen to make sure that people wait long enough. That is why I say 7 days when patients ask me how long it takes to be effective. The best physician for you to see about this problem is your OB/GYN or whoever administered the shot. They will probably ask you to also use a condom to prevent sexually transmitted infections as the Depo Shot will not protect you against those.
This answer is for general informational purposes only and is not a substitute for professional medical advice.
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