I recently discovered the book Marihuana Reconsidered written by physician Lester Grinspoon, father of astrobiologist David Grinspoon. Included in the book is an essay by Carl Sagan (who wrote under the pseudonym “Mr. X”) describing his experiences and opinions on the use and legal status of the drug.

I had reached a considerably more relaxed period in my life–a time when I had come to feel that there was more to living than science, a time of awakening of my social consciousness and amiability, a time when I was open to new experiences.
…
I do not consider myself a religious person in the usual sense, but there is a religious aspect to some highs. The heightened sensitivity in all areas gives me a feeling of communion with my surroundings, both animate and inanimate. Sometimes a kind of existential perception of the absurd comes over me and I see with awful certainty the hypocrisies and posturing of myself and my fellow men. And at other times, there is a different sense of the absurd, a playful and whimsical awareness. Both of these senses of the absurd can be communicated, and some of the most rewarding highs I’ve had have been in sharing talk and perceptions and humor.

Cannabis brings us an awareness that we spend a lifetime being trained to overlook and forget and put out of our minds. A sense of what the world is really like can be maddening; cannabis has brought me some feeling for what it is like to be crazy, and how we use that word ‘crazy’ to avoid thinking about things that are too painful for us. In the Soviet Union political dissidents are routinely places in insane asylums. The same kind of thing, a little more subtly perhaps, occurs here: ‘Did you hear what Lenny Bruce said yesterday? He must be crazy.’ When high on cannabis I discovered that there’s somebody inside in those people we call mad.

Sagan contends that his appreciation for art and music is enhanced while high, and he also admits that on occasion a cannabis high contributed to his new insights in both the social and physical sciences. Scientist that he is, Sagan took careful steps to ensure that his thoughts and experiences while high were not delusional, such as recording detailed taped messages for himself in the morning. His experiments seemed to convince him that insights while high are still valid.

I am convinced that there are genuine and valid levels of perception available with cannabis (and probably with other drugs) which are, through the defects of our society and our educational system, unavailable to us without such drugs. Such a remark applies not only to self-awareness and to intellectual pursuits, but also to perceptions of real people, a vastly enhanced sensitivity to facial expressions, intonations, and choice of words which sometimes yields a rapport so close it’s as if two people are reading each other’s minds.

Finally, Sagan suggests (what I consider) a reasonable measure for the safety of psychedelic substances:

I think the ratio, R, of the time to sense the dose taken to the time required to take an excessive dose is an important quantity. R is very large for LSD (which I’ve never taken) and reasonably short for cannabis. Small values of R should be one measure of the safety of psychedelic drugs. When cannabis is legalized, I hope to see this ratio as one of the parameters printed on the pack. I hope that time isn’t too distant; the illegality of cannabis is outrageous, and impediment to full utilization of a drug which helps produce the serenity and insight, sensitivity and fellowship so desperately needed in this increasingly mad and dangerous world.