PubMed-search found studies investigating adverse effects of combined oral contraceptive pills (COC) among teenagers. Four studies found a small negative impact of COC on acquisition of bone mineral density. COC is associated with elevated risk of venous thrombotic events (VTE), especially during the first year of usage. VTE risk increases with EE dose and progestin of 3rd and 4th generation. There are several difficulties in studying COC use in teenagers: high dropout rates, ethical considerations and many different COC formulas.