I asked a doctor about finasteride a month ago.
He said that finasteride is the prostate cancer version, whereas propecia is the version for hair loss (incorrect). He then told me they would need to order blood tests to know if my hair loss is due to androgens or malnutrition -- also incorrect given the recognizable pattern. He then said sometimes doctors prefer patients take minoxidil. Finally he said hair loss is genetic, and in studies propecia helps one third of people, has no effect on another third, and makes things worse for the last third, so it's not an effective drug (incorrect).
I did not bother arguing with him.