While COCs containing 20 μg EE may be theoretically safer, this review did not focus on the rare events required to assess this hypothesis. Data from existing randomized controlled trials are inadequate to detect possible differences in contraceptive effectiveness. Low-dose estrogen COCs resulted in higher rates of bleeding pattern disruptions. However, most trials compared COCs containing different progestin types, and changes in bleeding patterns could be related to progestin type as well as estrogen dose. Higher follow-up rates are essential for meaningful interpretation of results.
Comparative profiles of reliability, cycle control and side effects of two oral contraceptive formulations containing 150 micrograms desogestrel and either 30 micrograms or 20 micrograms ethinyl oestradiol.
To compare two oral contraceptive pills, both containing 150 micrograms desogestrel, but with either 20 micrograms (Mercilon) or 30 micrograms (Marvelon/Desolett) ethinyl oestradiol (EE), regarding reliability, cycle control and side effect profile.
                A double blind, randomised, multicentre study over one year with follow up after three, six and 12 months. The women noted tablet intake and all bleedings on specifically designed diary cards.
                University clinics, central hospitals and private gynaecological practices in Norway, Sweden and Denmark.
                One thousand women aged 18 to 40 years requesting oral contraceptive pills.
                Reliability, cycle control, side effects, blood pressure, body weight and haemoglobin.
                In a total of 4543 cycles with the 20 micrograms EE dose pill and 4688 cycles with the 30 micrograms EE dose pill, the number of pregnancies ascribed to method failure were 0 and 2, respectively. Irregular bleeding (break-through bleeding or spotting) was significantly more frequent with the 150/20 combination in about two-thirds of the cycles randomly distributed over the one year of the study. Mean blood pressure decreased slightly, particularly in the group on the 150/20 combination (about 1 mmHg), whereas mean body weight increased approximately 0.5 kg in the group with the 150/30 combination after 12 months. Haemoglobin did not change. Side effects other than bleeding problems were rare, but dizziness and mood changes were more frequent in the group on the 150/20 combination. Due to side effects, more women on the 150/20 combination discontinued the study during the one to three and four to six month periods, and women on this pill were also less positive about continuing the study drug at the end of the trial.
                Both pills have high contraceptive reliability and are well tolerated, but with the 150/20 combination the cycle control is less effective. However, in view of the potentially increased safety profile of the 150/20 combination, many women can be expected to accept some additional discomfort due to irregular bleeding.