People who lose height generally do so due to loss of cartilage in the spine, and various degeneration of bone (spine, knees, etc.) and muscle structure which causes slumping (not just slumping over). Doesn't take but a bit of that to knock an inch or two off your height, which is generally about as much as most people will ever lose. Lots of hormonal problems to worry about, but losing true height from even several few years of finasteride would be exceedingly unlikely. I've never even heard of men undergoing sex change and heavily modifying their hormonal profile losing height as a result.