Sentence: These results indicate that low-dose 100 microg levonorgestrel and 20 microg ethinyl estradiol given for 21 days is effective in suppressing ovarian activity and they confirm the contraceptive efficacy observed in clinical trials ( Pearl index of 0.8 ) .
Drug combination annotation:
[{'class': 'POS', 'spans': ['levonorgestrel', 'ethinyl'], 'is_context_needed': False}]