I'd like to reproduce a patented hair-restoring product under a
generic label. Is this legal? What kinds of legal hurdles will I face,
if any?

Don't do it, Katie!

If the patent holder catches up with you, they'll take you to the cleaners.

No. This is the point of a patent - to protect the holder of the
patent from other people using his technology.

It doesn't matter that you would be using a different name for the
product - you will still be infringing his patent.

Are you sure the patent is still in force and hasn't expired (i.e. all
renewal fees have been paid etc).

Also, there are often ways of getting around a patent by, for example,
substituing one feature of the invention for another.

If you post the patent number, I'm sure we could give you suggestions
on how to proceed.

You do it the same way there are generic products for every other name
brand out there.  You pay a licencing fee to the patent holder!!!