When someone starts a new hormonal birth control method for the first time, they need to use a back-up method or abstain for the first week. After that first week, the hormones are integrated into the body and will start to protect against pregnancy.
With that being said, if you are replacing the Nexplanon (formally known as the Implanon), you don’t necessarily need to wait another week before you’re protected.
If you had the new Nexplanon inserted while the old Implanon was still active (within 3 years of the insertion), you do not need to wait a week before the hormones kick-in. If this was the case, you are automatically 99% protected from pregnancy.
If you got the new Nexplanon inserted after the old Implanon had expired (more than 3 years after insertion), then you do need to abstain or use a back-up method for 1 week. If this were the case, it would be like starting a new method and the hormones need to be re-integrated into the body.
If you are not sure of the exact dates, contact the doctor’s office that inserted the Nexlpanon. They can give you concrete information on when the method will be effective.