Does nuvaring still prevent pregnancy if a man cums inside of you?

Yes, NuvaRing should prevent pregnancy even if you don't use any other precautions.

How should I use NuvaRing?

Use NuvaRing exactly as it was prescribed for you. Do not use the medication in larger amounts, or use it for longer than recommended by your doctor. Follow the directions on your prescription label.

NuvaRing comes with patient instructions for safe and effective use. Follow these directions carefully. Ask your doctor or pharmacist if you have any questions.

Your doctor will tell which day of your menstrual cycle to insert the first vaginal ring you use. During the first 7 days of using your first vaginal ring, you may need to use back-up birth control, such as condoms or a spermicide. Follow your doctor's instructions.

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The NuvaRing vaginal ring should be left in place for 3 full weeks. Remove the NuvaRing after 3 weeks, on the same day of the week it was inserted at about the same time of day. Allow 1 full week to pass before inserting the new ring.

Your period should start during the week you do not wear a vaginal ring. Insert the new ring on the same day of the week it was inserted in the last cycle, even if your menstrual period has not ended yet.
The NuvaRing vaginal ring will not prevent pregnancy if you wear it only during intercourse. You must wear the NuvaRing for 3 full weeks, followed by 1 full week without a ring. The timing of ring insertion and removal is very important for this medicine to be effective as a form of birth control.

the NuvaRing does not need to be removed during sexual intercourse. Neither partner should be able to feel the NuvaRing when it is in place. If the NuvaRing is bothersome, you may remove it, rinse it with warm water, and reinsert it after intercourse. Do not leave the NuvaRing out for longer than 3 hours.

To dispose of a used vaginal ring, place it in the foil pouch it came in and throw it away where children and pets cannot get to it. Do not flush the NuvaRing down a toilet.

Have regular physical exams and self-examine your breasts for lumps on a monthly basis while using estradiol vaginal.

http://www.drugs.com/nuvaring.html