Implanon contraceptive implant examined
Huynh Nguyen Khanh Trang (2007)
Mearns Leader [stonehaven (UK)] 17 Mar 2013.
Effectiveness and safety of the new contraceptive one-rod implant Implanon®
Hoang Thi Diem Tuyet
Use of the contraceptive implant beyond the FDA-approved duration (2014)
C. McNicholas
R. Maddipati,
G. Secura,
J. Peipert
(This study suggests that the rod may well be useful beyond the 4 year limit).
Metabolic effects of contraceptive implants in adolescents ☆ (2011)
Cristina A.F. Guazzelli, ,
Flaviano Teixeira de Queiroz,
Marcia Barbieri,
Fernando A. Barreiros,
Maria Regina Torloni,
Fabio F. Araujo
(The one above even states that the implant doesn't increase any chances of long term cardiovascular diseases, instead, it makes some girls a bit chubby - the horror).
A lot of the literature that I see points out that it's actually quite beneficial to the health of a female. You're going to need to link me to those studies you were referring to.
ETA: I apologise for the formatting of the post; it doesn't seem to agree with links from articles being posted.