Basically it seems the consensus is that everyone who used drugs and psychedelics at some point realized it was hindering their progress and so stopped using them. So far we all agree that drugs of many sorts can be of limited benefit, but not ultimate benefit since they cannot in themselves lead to realization.
Pot has the benefit of loosening the mind, relaxing the mind, and allowing new concepts and creative ideas to form. It has the side effect of placing perhaps undo importance on those concepts and ideas, and the additional danger of simply becoming a pothead. In my own experience, the most fruitful points of smoking pot has been when I haven't done it in a long time. After a few days of doing it, that effect wears off, and I find myself eating Nachos and playing video games.
LSD has the benefit of showing us that the minds perceptions and projections are mutable and ultimately unreal. It has the side effect of placing extreme importance on the projections that arise while tripping, despite that its not what appears that is important, but the fact that it *can* appear that brings upon this realization. The danger is that one begins to think that the crazy thoughts and appearances on LSD are somehow signs of realization or spiritual progress, but they are nothing more than mental fabrications entrenching one further into samsara. In my own experience the best LSD trips I've had are again when I was not using it a lot. When it was purchased with the specific intent to gain insight into my situation and self, done with that intent, and then let go, that was when I derived the most benefit from LSD, personally at least.
Mushrooms have the benefit of opening us up to our feelings more. Although it can also inspire creativity or insight into minds mutability, its the emotional aspect that has the biggest impact on our lives.
In general each drug effects different chakras. Pot is focused in the three lower chakras, which is why food, sleep and sex become central focuses of people who are high. Mushrooms effect the solar plexus and heart chakra due to its association with feelings. LSD is primarily the upper three chakras. Methamphetamine effects the throat chakra, a lot. Hence one stops wanting to eat and wants to talk, a lot. Any form of MDMA tends to also effect the solar plexus and heart chakra, which is why its now being used in small amounts in therapy (in addition to mushrooms, actually). Alcohol tends to effect the sex, solar plexus and heart chakra in different ways, although it tends to always cause some negative manifestation when done in excess (whisky dick or irresponsible choices in partners or unsafe sex, bouts of anger or sorrow, or extreme expressions of love towards people you may not know at all).
Its a path of skill in means, but one that few can follow responsibly. Its very easy to get caught in the trap of thinking drugs are enlightening you. I've seen it happen a lot in the "psychonaut" community. They always talk about how, whoa man, my third eye was like "pssshhh!". Yet they actually have no real insight to offer anyone and their words tend to just be egocentrically focused, realizing profound truths that are commonly available to anyone who can read, and easily known to anyone who applies themselves to practice. They also do not go on to be of benefit to anyone in a major way. Although some of them loosen some of the knots in the heart chakra and so forth and so become more generous or loving people, they are still heavily afflicted and their lives also tend to have an extra dose of drama to them as a result of the company they may keep.
I have yet to meet anyone who is like "I realized the nature of ultimate reality last night while on LSD" and then actually have this realization match up with their subsequent actions and so forth and be of permanent benefit to themselves and others. I've never met a single person who eliminated suffering from drug use, most of them just increase it for short or long periods of time. If anyone knows of such an example, I would be interested in hearing of it because I don't think its impossible.
Only stories of Mahasiddhas come to mind, but how are we to really hope to be as realized as them? Besides which, they also say their realization is due to the Guru, and not to drugs.