i think if you have had it put in while on your period you are protected straight away but dont quote me on this. i had mine taken out today after 3 years. which was not as easy as having it put in!!! we used protection for 14 days just to be sure. i had no problems with mine at all though i did not get a period for 15mths which was wonderful!!!! though i kept doin pregnancy tests to be sure.
any other info you want about the implant just yell
Works straight away as far as I recall but this was a while a go.
By far and away my best birth control method but alas conflicted with my PCOS so I had to have it taken out a year later but I absolutely adored it as far as contraception goes.