A systematic review by Pastor et al. «Pastor Z, Holla K, Chmel R. The influence of combi...»1 assessed 36 studies from 1978–2011. These studies included 11 uncontrolled follow-up studies, 8 controlled follow-up studies, 6 randomised controlled studies, 6 retrospective controlled studies and 5 retrospective uncontrolled studies. The review covered 13,673 women of fertile age from the United States, Canada, Europe and Asia. Eighty-five per cent (85%, n = 8,422) of combined oral contraceptive users reported an increase in libido or no change in libido. Fifteen per cent (15%, n = 1,238) reported decreased libido.
No significant differences were observed between pills containing 20 µg to 30 µg of ethinylestradiol. Only 15 µg pills caused a decrease in libido.
A systematic review by Davis et al. «Davis AR, Castaño PM. Oral contraceptives and libi...»2 assessed 30 original studies from 1966–2004. The review covered published English-language studies on women. The material comprised data on 5,880 women. The countries represented were the United States and Canada; Finland, Sweden, Switzerland, the Netherlands and Scotland; and several other countries including Venezuela, Puerto Rico, Haiti and the Philippines.
Out of these, the results of 17 retrospective, uncontrolled studies stated that women reported an increase in libido during the use of combined oral contraceptives. In 4 uncontrolled follow-up studies, the majority of women reported a small change in libido. Similarly, in 4 cross-sectional follow-up studies women reported both increased and decreased libido compared to women not using combined oral contraceptives. In 5 randomised, placebo-controlled studies, users of combined oral contraceptives were found to have decreased libido compared to those using placebo pills.
All in all, women experienced positive and negative changes in libido and unchanged libido when using combined oral contraceptives.