They actually can. Not the molecules themselves, but a specific formulation of it, that according to their studies, is somehow better that what existed before.
Adderall is just Amphetamine, that it has been known for decades didn't stop the patent. That's because it is a specific formulation.
Janssen Pharmaceuticals managed to find a way to get a patent on ketamine with Spravato. I'm sure a clever scientist will find a way to patent some aspect of Cannabis once it's rescheduled.
Adderall is just Amphetamine, that it has been known for decades didn't stop the patent. That's because it is a specific formulation.