Lower dosages of EE also have significant antigonadotropic effects. A "very low" dosage of 15 µg/day EE has been described as the "borderline" amount required for suppression of LH and testosterone levels in men, and a study found that LH and testosterone levels were "reliably" suppressed in men by a dosage of 30 µg/day EE. However, other clinical studies have found that 20 µg/day EE increased testosterone levels by 50% in men (as described above) and that dosages of 32 µg/day and 42 µg/day EE suppressed FSH levels in men but did not significantly affect LH levels. A stronger suppression of testosterone levels was observed in men following daily treatment with a combined oral contraceptive containing 50 µg ethinylestradiol and 0.5 mg norgestrel for 9 days. However, investigation revealed that the progestin was the more important component responsible for the suppression in testosterone levels. In accordance, the progestin component of COCs is primarily responsible for inhibition of ovulation in women. A combination of 20 µg/day EE and 10 mg/day methyltestosterone was found to suppress FSH secretion in men to an extent sufficient to stop spermatogenesis. Studies in women have found that 50 µg/day EE suppresses LH and FSH levels both by about 70% in postmenopausal women.