A while back Dr. David Gorski wrote a series of posts at Science Based Medicine on medical marijuana as “ the new herbalism.” In the introductory post he discussed the scientific problems with herbalism in general and I think he really nailed it with this:
I also pointed out that, although herbalism is the most plausible (or perhaps I should say the least implausible) of modalities commonly associated with “complementary and alternative medicine” (CAM) or “integrative medicine”, it still exhibits a number of problems, the biggest of which is what I like to call either the delivery problem or the bioavailability problem. In brief, herbs, when they work, are adulterated drugs. The active ingredient is usually a minor constituent, embedded in thousands of other constituents that make up herbs, and it’s almost impossible to control lot-to-lot consistency with respect to content or active ingredients given how location, weather, soil conditions, rainfall, and many other factors can affect how the plants from which the medicines are extracted grow and therefore their chemical composition. To demonstrate the concept, I pointed out that it’s much safer and more predictable to administer digoxin to a patient who needs its activity on the heart than it would be for the patient to chew on some foxglove leaves, given that the therapeutic window (the difference between the doses needed to produce therapeutic effects and the lowest dose that will cause significant toxicity) is narrow.
It's basic. It's a major premise, a starting point for discussions of herbal medicine.
The degree of evidence in support of the medical use of marijuana is somewhere between slim and none, so why such wide acceptance? As Dr. Gorski suggests:
Indeed, more than twenty states, plus the District of Columbia, have legalized medical marijuana. They’ve done so on the basis of a political movement among patients that make pot sound like a miracle drug that can help when no other intervention can. And it’s more than that. Medical cannabis has been touted as a near-panacea for everything from pain to chemotherapy-induced nausea to HIV- and cancer-induced cachexia to even curing cancer itself. Yes, there’s a lot of hype out there, and there are a lot of claims that sometimes go viral on various social media, even though the evidence to support the claims is often, to put it mildly, less than rigorous.
It's just another example of how, when issues of science are determined in the arena of public discussion hype all too often wins.
Although I'm not a proponent of legalization of marijuana for recreational use it is hard to disagree with Gorski's position:
Again, I believe that marijuana should be legalized, regulated, and taxed, just like alcohol and tobacco. If marijuana is going to be approved for use as medicine rather than for recreational use, however, the standards of evidence it must meet should be no different than any other drug, and for the vast majority of indications for which it’s touted medical cannabis doesn’t even come close to meeting that standard.
Put another way, an argument for legalization for recreational use has far more integrity than an argument for medical use.
Dr. Gorski summarizes the evidence in this manner, and this comports with what I have seen:
Overall, the evidence base, from my interpretation, ranges from nonexistent (most indications) to suggestive (anti-inflammatory), to fairly good (ant-emetic). However, most of the good clinical trials didn’t use marijuana cigarettes as most patients get them, but rather either purified cannabinoids (or synthetic analogues) or cannabis cigarettes spiked with varying amounts of THC. Indeed, all of these studies tend to suggest that purified drugs from cannabis or synthetic drugs based on compounds designed to mimic either endocannabinoids or cannabinoids from marijuana will be the future. I realize that that’s not what medical marijuana activists want to hear.
So all this is not to say that cannabinoids have no medical potential. Indeed they do. They have intriguing biologic effects that warrant investigation. But all scientific indications point to pharmaceutical grade cannabinoids rather than medical cannabis. As Gorski further states:
In any case, if one were going to decide on a drug delivery device for cannabinoids, one could hardly design a worse device than burning the leaf and inhaling the gases, where the active drug is just one of hundreds of products of combustion, all loaded with particulate matter and tar.