Why are there few controlled studies of the effect of THC on humans been done?

There are various reasons for this. Marijuana, and also THC, has had the stigma of being an illicit substance for quite some time. USA, who could've been the leader within science and technology, has had an extremely conservative drugpolicy for over 70 years and due to this the amount of research done and tests conducted has been extremely limited by the federal government, as every test needs an approval from them. Additionally, the marijuana that you would have to conduct the test with has to be supplied to you by the federal government, and you can imagine that they're probably not too happy about that. This whole ordeal has virtually excluded the United States of America from the scientific front on these matters and then you're left with Europe alone to conduct such studies.

There are also probably more reasons, but the shear reason that people like Ronald Reagan claimed it to be "one of the most harmful drugs in use today" would make it hard for people to get a permit to conduct these studies. Can you imagine what would happen it if turned out that the research showed that marijuana didn't make you insane? Ibelieve Reagan made a similar statement was because marijuana was considered to be a "gateway "drug that led to abuse of harder drugs. All drugs came from nature, or are synthesized from the natural drugs. All drugs have the potential for good use or abuse. Not only was there cocaine in Coca-Cola{used like Lydia Pinkham's Tonic for Women's Complaints] theyalso marketed cigarettes in the 1920-1930'scalled Asmadors. You could get them at you corner drugstore. They were great for stupid asthmatics who chose to smoke.THC is a bronchodilator, which expands the alveoli{littltesacs} in your lungs.With chronic pulmonary disease, these little sacs loose their elasticity so you feel as if you never get a deep breath. The Asmadors helped.But they also gave you a buzz and made Granma complain they made her dizzy. So a promising treatment for astma was outlawed and buried, I believe there are pills now with THC, but not as effective as the smokable variety. I don't advocate recreational drug use of any kind,but if I am terminally ill I want to be strung out at the end.God giveth the drugs and the Government takes them away.