I have no opinion about medical cannabis. But recreational, oh yes. The OP wanted to address this from a Torah perspective. I will try to keep to that.
There is not a question that marijuana is a mind altering substance. If it was as benign as a slice of cucumber, there would have never been discussion.
Question #1. Is there a heter to alter one’s mind? At all times, a Yid is obligated to be an oveid Hashem, whether in the midst of learning, davening, and even going through the mundane parts of one’s daily existence. While lofting away under the THC laden smoke, it is a tough sell to say that one is aware of HKB”H. The euphoria one experiences is not the product of ‘ אז תתענג על ה, but a chemically induced neurological state. That is not to be confused with Avodas Hashem. I have heard some young people claim to “learn Gemora better when under the influence”, but that is so absurd is laughable.
Question #2. Is there a threat to health? Great question, though most people first provide the answer they want, then go backwards to justify it. There is a very different toxicity from marijuana than most other drugs. There is no risk of overdose. The degree of impairment while “high” is both different from other drugs, and less dramatic. It does not normally trigger getting wild. We can list many other things it does cause. But it is important to examine what it does do. Research indicates it is a serious gateway drug. It impairs reaction time, making driving and operating machinery a risk. It affects a great many internal organs, and is stored in fat cells as well as those making up many organs and glands. The MJ remains in the cells for periods up to several weeks, and its effects at the cellular level continue until it is somehow excreted. It can impair fertility. I have met people whose pancreas was affected, and are now insulin dependent diabetics. I have met people whose voice and other gender specific characteristics have changed because of impairment to their glands. If tobacco smoking poses risk to the lungs, MJ is several hundred times more dangerous. Considering the mitzvah of ונשמרתם מאד לנפשתיכם, MJ poses a huge problem.
Question #3. Is there anything wrong with being high? The Rambam specifies that mitzvos, including learning and davening, that are performed while intoxicated are not mitzvos at all, and are actually abominable.
Question #4. If marijuana is not addictive, is it less dangerous that alcohol and tobacco, both which seem to be quite widely accepted in the frum community? The problem is the word “addictive”. If one is looking for physical dependency, that would be characterized by tolerance and withdrawal, no. But addictive means much more than that. Becoming accustomed to dealing with life by escaping into a world of another brain state is actually quite terrible and frightening.