haʊˈɛvɚ, ɔːlðˈoʊ ɪfˈɛktɪv, ðə pɹˈɛɡnənsi ɹˈeɪt ɪnðə lˈɑːɹdʒɪst stˈʌdi kəndˈʌktᵻd wʌz fˈoːɹ.sˈɪks pɜː wˈʌnhˈʌndɹɪd wˈʊmənjˈɪɹz, wˌɪtʃ ɪz tˈuː hˈaɪ əvə fˈeɪlɪɹ ɹˈeɪt fɚðə mˌɛdɪkˈeɪʃən təbi ɹˌɛkəmˈɛndᵻd æz ɐ sˈeɪf mˈɛθəd ʌv bˈɜːθ kəntɹˈoʊl.
However, although effective, the pregnancy rate in the largest study conducted was 4.6 per 100 woman-years, which is too high of a failure rate for the medication to be recommended as a safe method of birth control.