Finasteride / Dutasteride work by inhibiting enzyme 5α-reductase.
Potential common ( >1% ) side effects include:
>Shrinking penis
>Erectile dysfunction
>Loss of all sexual or romantic desire
>Anhedonia (lack of pleasure)
>depression
>suicidal thoughts
Symptoms persist permanently in 1/3 of cases.

How to Look Up the Money Your Doctor Is Getting From Big Pharma:
https://openpaymentsdata.cms.gov/
(not counting under the table kickbacks)