The oral bioavailability of norethisterone is between 47 and 73%, with a mean oral bioavailability of 64%. Micronization has been found to significantly improve the oral bioavailability of norethisterone by increasing intestinal absorption and reducing intestinal metabolism. A single 2 mg oral dose of norethisterone has been found to result in peak circulating levels of the drug of 12 ng/mL (40 nmol/L), whereas a single 1 mg oral dose of norethisterone in combination with 2 mg estradiol resulted in peak levels of norethisterone of 8.5 ng/mL (29 nmol/L) one-hour post-administration.