Yes, there was a total ban on all medical research on cannabis until very recently, scheduled by the FDA as having no medical benefits, therefore no research allowed. Still in effect at the federal level in the US, which means enforced in most countries. Technically still illegal, it's just not always enforced. Most countries still do not allow any research at all, explicitly forbidden under threat of significant sanctions from the US government. There has been exactly one federal research project a few decades ago and it was ended. There are hundreds of cannabis strains, recreational cannabis is not at all a good comparison. It can't be compared to a single chemical substance like alcohol or cocaine, there are hundreds of chemical compounds involved. Almost all the research has been done in secret, like how some specific strains were discovered to help with some forms of epilepsy, no research lab was involved in this, all illegal. I mean pain research in general is very poor, it can "show evidence" that singing to yourself is good, or whatever is popular these days. Most of it is just uninterpretable so not much surprise that what little research on cannabis would be poor as well, it all is. In addition to having been forbidden for decades, of course. That doesn't help. There is no evidence in research that ME is a relapsing-remitting illness. And yet it is. That scientific research doesn't show it doesn't mean much, frankly, if the right questions aren't asked.