If the Federal government (using taxpayer money) decided to buy a drug from a particular pharmaceutical company and gives it out free, what incentive is there for a competing company to develop a better drug?
If the government is giving away free Fords, what happens to Chevy?
Incidentally, the idea that the obesity epidemic is going to be solved with a new weight loss drug may be a bit naive.
The US has nothing close to "free market" health care. The only areas of medicine that are somewhat "free market" are elective surgeries and procedures, and in these areas, the quality is arguably the best in the world, and the cost are very competitive.
I did not see an article in your post, but it would add noting to the discussion either way.