Review of subdermal implantable contraceptives (News-Medical-Net)
A Cochrane Systematic Review that set out to assess the effectiveness and tolerability of subdermal implantable contraceptives compared to other reversible methods of contraception found that they were all good at preventing pregnancy.

Study Of Contraceptives Finds Implanon, Norplant And Jadelle Are All Effective But Side Effects Vary (Medical News Today)
A Cochrane Systematic Review that set out to assess the effectiveness and tolerability of subdermal implantable contraceptives compared to other reversible methods of contraception found that they were all good at preventing pregnancy. No one subdermal implant was found to be any more or less effective than the others in preventing unwanted pregnancies. [click link for full article]