Can methods of production involving cannabis be patented?

Section 101 of Title 35 U.S.C. sets out the subject matter that can be patented:

Whoever invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent therefor, subject to the conditions and requirements of this title.

The meaning of these words has been interpreted over the years through a combination of court cases and USPTO guidance, and method claims (synonymous with “process” in the statute quoted above) are generally patent eligible. Patents that claim methods have grown in popularity over the years to the point that a majority of new patents include at least one independent claim that is directed to a method or process.

But how do patent rules interact with federal cannabis prohibition? At present, there is nothing explicitly stated in patent laws that bars patent protection for illegal substances. In the wake of legalization of cannabis for recreational use in several states, many entrepreneurs have been working hard to protect their new, cannabis-related inventions. But the practice of patenting cannabis-based inventions long-predates recreational legalization. For example, in 2002, this patent protecting cannabinoid extraction methods was issued. (It is important to note that patent protection does not afford the inventor the right to use his own invention—it affords him the right to exclude others from use, and it does not generally modify the scope or application of criminal laws.)