That really depends on your age, medical specialty, and other factors.
If you pay using cash or securities, then yes it's probably a good investment. If you invested that same money in the stock market over 8 years (@ 8%APR) that money would be worth 300K (in today's dollars). So if you're entering a competitive specialty, you can probably make the 140K up quickly. If you're entering family practice, not so much.
If you use loans, it really depends on the rate. I don't know where you're going to get a 160K lump sum loan... but if you did, you could get tax breaks on the interest and it would reduce your tax liability over the life of the loan...
So go for it, but you better work your tail off in med school so you can get paid...