Birth control pills with 20 µg estrogen versus more than 20 µg estrogen

Concerns about safety have led to making birth control pills with less of the hormone estrogen. Pills with less estrogen might not work as well to prevent pregnancy and could cause bleeding problems. This review looked at studies that compared pills with 20 µg ethinyl estradiol versus pills that have more estrogen.

In July 2013, we did computer searches for randomized trials of pills with 20 µg estrogen versus more estrogen. We did not find any new trials. For the initial review, we also wrote to researchers and makers of birth control pills to find other trials.

Studies had to be written in the English language, include at least three cycles, and focus on birth control. The trials had to report on pregnancy, bleeding problems, or stopping the pills early. We also looked at side effects.

More women taking the pills with less estrogen quit the studies early. The women on less estrogen also had more bleeding problems than those taking pills with more estrogen. Pregnancy rates seemed to be the same between groups, but the studies may not have been large enough to know for sure. This review did not focus on the rare events needed to test whether birth control pills with 20 µg estrogen were safer. Also, most trials compared pills with different types of the hormone progestin, which could also affect bleeding patterns. The high losses in many trials make the results hard to interpret.

Authors' conclusions: 

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.

Read the full abstract...

Concern about estrogen-related adverse effects has led to progressive reductions in the estrogen dose in combination oral contraceptives (COCs). However, reducing the amount of estrogen to improve safety could result in decreased contraceptive effectiveness and unacceptable changes in bleeding patterns.


To test the hypothesis that COCs containing ≤ 20 μg ethinyl estradiol (EE) perform similarly as those containing > 20 μg in terms of contraceptive effectiveness, bleeding patterns, discontinuation, and side effects.

Search strategy: 

In July 2013, we searched CENTRAL, MEDLINE, and POPLINE, and examined references of potentially eligible trials. We also searched for recent clinical trials using and ICTRP. No new trials met the inclusion criteria. Previous searches included EMBASE. For the initial review, we wrote to oral contraceptive manufacturers to identify trials.

Selection criteria: 

English-language reports of randomized controlled trials were eligible that compare a COC containing ≤ 20 μg EE with a COC containing > 20 μg EE. We excluded studies where the interventions were designed to be administered for less than three consecutive cycles or to be used primarily as treatment for non-contraceptive conditions. Trials had to report on contraceptive effectiveness, bleeding patterns, trial discontinuation due to bleeding-related reasons or other side effects, or side effects to be included in the review.

Data collection and analysis: 

One author evaluated all titles and abstracts from literature searches to determine whether they met the inclusion criteria. Two authors independently extracted data from studies identified for inclusion. We wrote to the researchers when additional information was needed. Data were entered and analyzed with RevMan.

Main results: 

No differences were found in contraceptive effectiveness for the 13 COC pairs for which this outcome was reported. Compared to the higher-estrogen pills, several COCs containing 20 μg EE resulted in higher rates of early trial discontinuation (overall and due to adverse events such as irregular bleeding) as well as increased risk of bleeding disturbances (both amenorrhea or infrequent bleeding and irregular, prolonged, frequent bleeding, or breakthrough bleeding or spotting).