After the discovery, in the early 1990s, of specific G-protein-coupled receptors for marijuana's psychoactive principle Delta(9)-tetrahydrocannabinol, the cannabinoid receptors, and of their endogenous agonists, the endocannabinoids, a decade of investigations has greatly enlarged our understanding of this altogether new signalling system.
I finished medical school in 1986, so my core medical sciences ended in 1983, about 21 years ago. The endocannabanoids, endogenous (natural) agents that act on the same neuro receptors as cannabis, feel like the most dramatic new discovery since that time. Researchers long suspected that, just as we have endogneous opioids, we must have endogenous cannabinoids. It just took a while to find them.
True, we did sequence the genome -- and that's been amazing. But, oddly enough, it felt like a continuation of what we new or guessed in the early 80s. New physiology feels more "real" and proximal to a physician. For example, I went to this research article because of hype about an endocannabinoid derived medication that allegedly helps with weight loss and smoking cessation. Talk about near term impact.
This feels new, and exceptionally interesting. I know nothing at all of the basic science, but I'll be looking for a "popular" (eg. physician oriented review) in JAMA or NEJM.
This probably also provides some insight as to why cannabis sativa manufactures its namesake product in the first place.