It's probably true that if the chemistry is identical between naturally and artificially produced material is the same, it would be covered by a patent based on its chemistry. The FDA however must accept the way commercial drugs are made, and they could easily not accept the material being extracted from cannabis, while they accepted the material being made through chemistry.

I'm certainly no expert here, but I know of drugs that were held out of the market for well over a year because the FDA didn't accept how it was being made, and even longer when the shelf life of the drug didn't meet FDA requirements.

In short, they don't care how much they increase the cost or time it takes to bringing a potentially life saving drug to market, it's their way, or no way.

Gary