How many years will finasteride be effective?

As long as you take it, it has value to maintain your hair, not necessarily restoring it, but slowing down the progressive nature of genetic hair loss. One patient comes to mind, he was 62 and has been on finasteride for 20+ years. He thought it was time to stop it and when he did, he lost hair and quickly went back on it. The few long term studies on it seem to reflect benefits on hair for long term use.