In its information, Propecia states that men need to take the pill at least 3 months before they will see any benefit. They also state that if you stop taking the treatment, on average it takes around 12 months for you to lose the hair you gained and start losing hair again. According to controled, open-extension studies that have been ongoing for 3 years, the effects of Propecia have been maintained.
In the combined studies on vertex baldness, the mean hair count changes in Propecia vs. Placebo were:
91 vs -19 hairs for Caucasians (1,185 men)
49 vs -28 among blacks (83 men)
53 vs -38 among Asians (17 men)
67 vs -15 among other ethnic groups (20 men)
In those who experienced sexually adverse side effects, the problems were resolved in all who stopped the treatment and in 58% of men who continued the therapy. The incidence of breast tenderness and enlargement were not different than those taking placebo.
Circulating levels of testosterone and estradiol increase 15% while on Propecia.
39% of finasteride metabolites are excreted in the urine; 57% in the feces
Excreted metabolites have 20% the 5-alpha reductase inhibitory activity of finasteride - meaning sickly enough your own excretions could be used to treat your hair loss
In a study of 15 healthy male subjects, the mean bioavailability of Finasteride 1mg tablets was 65%.
A study on bioavailability showed it was not affected by food.
Semen levels were measured in 35 men taking finasteride 1mg/day for 6 weeks. In 60%, finasteride was undetectable. The mean finasteride level was 0.26 ng/mL and the highest level measured was 1.52 ng/mL. Assuming 100% absorption from a 5-mL ejaculate per day, exposure through absorption in a woman would be up to 7.6 ng per day, which is 750 times lower than the exposure from the no-effect dose for developmental abnormalities in Rhesus monkeys.