How does "medical" differ from "medicinal"?

In 2005, I asked Merriam-Webster the following question. Life Sciences Assistant Editor, Chris Connor, replied as follows.

Q: Medical means “requiring or devoted to medical treatment.” Medicinal means “tending or used to cure disease or relieve pain.”

But doesn’t “medical treatment” necessarily mean “tending or used to cure disease or relieve pain.” In other words, how do medical and medicinal differ? The specific example I’m thinking of is medical vs. medicinal marijuana.

A: The difference in meaning between “medicinal” and “medical” is slight, although their use is not synonymous. The main difference in their use, in my opinion, is that “medical” denotes inclusion (“devoted to…”) in the practice of medicine, which is not necessarily the case with “medicinal.” The use of “medical” in the compound “medical marijuana” therefore indicates an acceptance of marijuana in “mainstream” medical practice.

This is not the case with “medicinal marijuana,” which only indicates that marijuana has positive health effects. A similar case can be seen with “medicinal herbs,” which is a much more common compound than “medical herbs.” Though used to cure disease and relieve pain, herbs are not typically a part of traditional Western medicine. They are medicinal but not medical. I sense that this is the slight difference that distinguishes “medical” from “medicinal.”