It's misleading to say that "nothing of significance" has been shown.
There were more than 1,000 peer-reviewed clinical papers detailing the use of psychedelic compounds (administered to approximately 40,000 patients) published by the mid-1960s.
LSD was seen to have a greater than 50% success rate in treating alcoholics in just a single-session:
Source: Smart RG, Storm T (March 1964). "The Efficacy of LSD in the Treatment of Alcoholism" (PDF). Quarterly Journal of Studies on Alcohol. 25: 333.
In addition, there are studies ongoing today: https://www.nytimes.com/2014/03/04/health/lsd-reconsidered-for-therapy.html
The founder of Alcoholics Anonymous, Bill Wilson said that, "I am certain that the LSD experiment has helped me very much. I find myself with a heightened color perception and an appreciation of beauty almost destroyed by my years of depression.”
This is just one use of LSD.
Maybe you will enjoy this TED Talk by a current research scientist:
that's like giving weed to tobacco smokers and claiming that it cures puffing.
Since nicotine addiction often is a self-medication for repressed trauma, weed might treat the underlying anxiety and stop the person smoking tobacco.
However, I think LSD would be more effective than weed for nicotine addiction.
Scientists have found that LSD will cure a person of tobacco addiction: http://www.newsweek.com/how-acid-helped-stop-smoking-413593
And other psychedelics are also effective at treating tobacco addiction:
http://www.bbc.com/future/story/20150615-could-psychedelic-drugs-make-smokers-quit
And:
https://www.theatlantic.com/health/archive/2016/06/live-like-youre-on-mushrooms/487286/
pets can cure tobacco addiction. exercise can do that as well.
addiction is not a substance problem. Is a human connection problem.