How effective is it?

The Implanon is 99.9% effective. It's immediately effective if inserted during the first 5 days of your menstrual cycle, which starts with the first day of bleeding.
The implant is effective after 7 days if it is inserted at any other time in the cycle.
If changing from the Pill or another method of contraception discuss the best time for insertion with your doctor.

The possibility of skin bruising after insertion and scarring after removal.