Doctor, unless you have been on finasteride 1mg daily for long term without any breaks and have dropped below baseline then I'm afraid these claims are unsubstantiated. My highly respected doctor in the NYC area who prescribed it to me said this is not the case for his hundreds of patients. Also, the finasteride 5 year and 10 year medical studies also don't show that you will lose ground (at least the vast majority.) Only 10% and 7% dropped below baseline respectively, and it's not like this minority of men went bald. They might have dropped a norwood level or two.
I am quite confused as to why some people on this forum believe this is the case. Maybe a patient's hair will get a bit thinner due to age related thinning while on the drug, but this won't happen until you're an old man if it happens at all. It's not like you're going to go completely bald in areas that you would had you never taken the drug.
Anyway, why should I take the time to argue with some of you guys on this forum? I have a full head of teenage thick hair because of the drug. Best of luck guys.