Here's why I point out the problem with even casual drug use. I thought of this analogy to explain how the brain works.
The brain is able to do a lot of things at once because it uses what you might think of as an inventory room in the back of a store, with shelves of products along lots of rows.
So the brain is constantly taking in all information (such as what you see, hear, read and also what your body is feeling) and shoving it as fast as it can in the right "slot" just as if it were an inventory stocker. Obviously one hopes that the brain identifies new incoming stock and puts it in the right place. For example, you see something, so the brain slots it in the shelf that handles seeing and not the shelf that handles tasting.
The brain then organizes the shelves and the aisles so it doesn't have to run all over to the most frequently used areas. This is the creating of paths.
Now, here's what a lot of people don't realize. Part of the genius of the brain is that at the same time that it puts the right information in the right place, it also experiments with putting it in the wrong place. That is actually an evolutionary survival advantage, not a problem. Most of the time humans never notice that the brain is doing this. So to use our example, once in while the brain takes something you see and rams it for a moment into the shelf that handles, let's say, past memories, or something even more "in error" such as you have the notion that you've had a religious experience (while you are actually looking at coffee grounds).
The reason the brain randomly but constantly "tries out" inappropriate stocking is that this is a source of rapid and creative breakthroughs in human thought processes. A random and wrong connection might actually have some valid application, in which case it will happen a few times to you and become a legitimate thought process and association.
But humans are not meant to glom onto one occurrence of the brain's "experimentation" because like I said, these are random wrong associations that the brain is just trying out once, and discards when it is not repeated with validation.
A lot of mental illness and spiritual foolishness results from people learning how to freeze frame their own brain's doing of this one time experimentation and concluding that they have been "enlightened" and have received "valid" information.
This is the source of a lot of people who have schizophrenic visions and thoughts, for example. They, through no fault of their own, have brains that latch attention onto the experimental slotting and shelving that all brains do, and make those linkages permanent.
Where it is people's own fault is when they practice, as in abuse, activities such as "meditation" and Reiki and other mind "techniques" because they think every stupid random thought that does go through their brain is mystical and "revealing" of an "inner truth."
Drugs make this a problem one hundred fold. Drugs slow down the mental process so that when one's brain randomly tries out a wrong slotting and shelving, you consciously notice it and think it is a valid perception and an appropriate thought process. So the brain cannot discard this one time experiment as it normally would, because you by focusing on it have now transferred it into short and then long term memory. Thus you mark it's place on the aisle and with each repeat of that perception you ratchet that location and association up in its stocking importance.
All brains do this, it is natural and mostly unnoticed, except when you have a really weird thought. But humans must let it go and not focus on it if you do actually notice it because to reinforce it by thinking about it and valuing it is to reinforce the erroneous connection that was never supposed to be made.
For example, one day you might see something blue colored and the brain might try out slotting that as being "the smell of a tree." It's not, and when the brain is at the same time putting it in its proper place as being a "color" the brain drops the goofy idea that maybe it was the smell of a tree. It's only if over time blue is really proven to be the smell of a tree that the brain lets that become part of its proper wiring.
Another time you might notice this is when you are about to fall asleep and you are not yet asleep but you start to have thoughts that go in strange directions. You may be thinking about your work day and then all of a sudden it turns into linking very different parts of your life in some strange way. That is the random slotting together with the dream time entry. There is no harm in it if you realize that is what it is and just forget about it.
But too many people "cultivate" every random thought (and worse, teach others to do so) thinking that they are "onto some message from the universe." All these people are doing is driving themselves and others neurotic. If continued it can be worse than neurotic.
I hope that you have found this analogy helpful.
See, by the way, while you were reading this, your brain would have been doing a few of the random error attempts, but you didn't notice because you were interested and fully absorbed in this topic. That is the way it should be. If there had been any value in a weird random error thought then you'll have it again some day and the brain will recognize its valid utility on its own, without you realizing it. People who are fully absorbed in something interesting or important (like reading my blog, ha) are protected from having these problems because the brain is doing its thing, unnoticed, as it should, just like you don't notice every heartbeat or breath.