In terms of its effects on individual humans, cannabis is a notoriously elusive plant. The same strain of weed will put one person to sleep, and make the next person feel energized and focused. One person will take one hit of pot and crumple into a ball of anxiety, and the next will smoke a bong load and be able to make a public speech.

This presents major challenges for researchers, most especially those trying to determine the health effects—both good and bad—of pot. Because weed remained illegal for so long (and still is a major crime according to the federal government), we are still in the very beginning stages of health research on pot. Even now, researchers find funding hard to come by, and must jump through all kinds of bureaucratic hoops to do their work.

As a result, despite the best efforts of pot researchers, we don’t yet have a lot of answers. We don’t really know what ill effects pot has. Just for one example, there are indications that pot use might damage the developing brains of adolescents, but we don’t have anything like a firm handle on how true that is, or what the effects might be.

We’re just as lost when it comes to the health benefits. There are indications that cannabis can act as a palliative for all kinds of different maladies, but in most cases, that’s all they are so far: indications. Not totally solid evidence.

The only health problems for which pot can be legally prescribed, according to the federal government, are certain kinds of seizures. The Food and Drug Administration in 2018 approved Epidiolex, a cannabis-derived pharmaceutical, for treating a couple of rare, but severe, forms of epilepsy.

Other than that, our knowledge—or rather, our lack of it—runs along a spectrum from the ludicrous (“pot will cure your brain cancer”) to the nearly certain. At the latter end of that spectrum, we have pretty solid evidence that cannabis can, in some cases, relieve pain more effectively, and certainly more safely, than narcotics do. It has also been known to help some people with anxiety disorders, even including post-traumatic stress disorder.

And cannabis has long been relied upon as a cure for nausea. That was one of its first recognized medical uses in fact: Even as far back as the 1970s, some doctors were telling chemotherapy patients they might want to try weed to alleviate their stomach sickness. And people were using it for that purpose for centuries before that.

But in every one of these cases—like in pretty much all cases—uncertainty abounds. Both cannabis and the people consuming it vary widely. Pot might help relieve PTSD, but it also might make it worse, depending on the person, the chemical makeup of the plant, the method of ingestion, etc. So many people have reported that cannabis relieves their pain that there can be no question that it’s effective—except when it’s not. Lots of people have reported that cannabis has zero effect on their pain.

Nausea might be the best example we have of the insane complexities surrounding pot as a palliative, and of how, depending on various factors, it can often cause and cure the same health problems in different people (and even the same people at different times).

Research issued last week gave us yet more evidence that cannabis is especially effective in relieving or preventing nausea and vomiting. But for some long-term users, cannabis seems to be a cause of nausea and vomiting. Cannabis hypermesis syndrome seems to be pretty rare, but it also seems to be real, despite what some knee-jerk pot advocates might say about it.

Such complexities abound in pot-health research. For that reason, it will be years and years before we actually know how and when to prescribe it, to whom and for what. And even then, it will likely take a lot of trial-and-error before individual patients find the right solutions for them. But then, that’s also true of a lot of the drugs that are prescribed every day, supported by tons of research.

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