There are two different aspects at play here with your description, and it's important that you see both of them.
One is the facticity of a situation, and this is valuable, so when you say the "stuff was dirty, impure, toxic, dangerous, and foul"
Something can be soiled, which would make it dirty (by adding another substance to it which degrades the purity of the original substance) so in that sense, a white cloth, once you add mud, can become "dirty"... but this is just the factual point. This is "Isness", just the observable nature of it, without adding any kind of emotional attachment. When dirt was added to the white cloth, you can say the "purity" or the whiteness, of the cloth was spoiled.
When we extrapolate this observation to something like marijuana, for example, there is nothing inherently "dirty" or "impure" about high-quality pot. Marijuana has its own effect. That effect is independent of you. How that effect is used, can go both ways... it can bring your consciousness down, or it can be used in a medicinal way, that depends on you and your understanding. If you just use it to get high, without awareness, you will lose "yourself", but that is not the fault of the pot, that is the fault of you and your lack of awareness. Unconscious acts create this "evil" that you speak of.
Another way we can look at dirty, is by observing the inflection in the word itself, like something is sub-standard, or is unworthy of you, or is below you, which in and of itself is a degrading aspect (semantics can get tricky here, I mean degrading in the synonymous sense of "less than" or "lower than", no emotional inflection implied, simply facticity of it) This emotional inflection can come from all kinds of places, and its important to understand this level very deeply. There is nothing inherently wrong in marijuana, but if you have been told, or somehow formulated the opinion that it is "dirty" with this emotional inflection, that it is somehow below you, then naturally you have already subconsciously made the decision "against" it (and this is how it becomes "evil" in your mind, because you feel like it's not devine, so your respect for it's divinity is already lost due to your preconception), because it's not worthy of you, so naturally even if you smoke to enjoy it you will not be able to, this will create guilt in your consciousness, because you are splitting yourself by smoking something that you believe, or have already made the conclusion, is not worthy of you. This is what I mean by "preconceived notions" and those can be very problematic.
Technically speaking, everything in life is just various forms, or manifestations, of the One Devinity (Call it nature, call it God, call it whatever you want) But, marijuana has both aspects, it can make you lose yourself, if you don't respect it, and use it unconsciously, or it can be used medicinally to help alleviate pain, or for appetite stimulation in patients that need it, or for glycoma patients to relieve pressure on the eyes (not sure about this, have never confirmed the truth of this statement about the glycoma, but its widely reported, so I assume the possibility, but do not know if true or untrue)
The same holds for most other drugs. Opium can be the biggest addiction in the world, and ruin lives, it can also be used as a pain killer after a major surgery to help the patient recover. LSD/Mushrooms can make you go crazy, if you eat too much or your consciousness is not compatible with those states of awareness (because of prior psychological issues, or other problems that do not agree with the trip) or it can be used for healing therapy as an etheogen to give deeper insight into problems from perspectives you may have not otherwise been able to see...
And so on and so forth.
The only thing I'm fuzzy on is things like crystal meth, I have tried it, but I do not see any kind of condition under which it would be beneficial... not to say one does not exist, but the nature of that substance is simply toxic and unhealthy, and it wastes so much of your energy and makes you unconscious, that one could say that it's mostly just bad for you.
Cocaine has been used in the medical field for decades, but it can also overstimulate you and kill you in large enough doses.
So, back to your statement of "because the stuff was dirty, impure, toxic, dangerous, and foul"
If you got "dirty, impure" marijuana, you need to talk to your guy about that 8) ... joking, but also not. :lol:
In any case the facticity of most drugs, the factual statement, is that most of them are toxic, and dangerous, and some of them can be foul, ayahuasca tastes terrible by nature, so you could say it's "foul". But if you're using the term "foul" to define its emotional content as a drug which is "bad" for you, then it's inaccurate, it would depend on your own consciousness how you perceive it. If you have the utmost respect for something, and use it consciously with full awareness, then there is nothing inherently "dirty, impure, or foul" about the substance (unless you dropped your weed on the ground, and it's laced with something, and tastes like crap, of course 8) )
So, if you use drugs unconsciously, you will lose yourself. If using drugs in any kind of way makes you lose yourself, then just stop using drugs, and you will have "yourself" back. Your system cleans itself, and removes toxins by itself, you don't have to do anything actively for that. Just drop these things that are making you lose yourself, you don't need to take another drug to find yourself. Can ayahuasca help? it depends on you, it has the potential to both help, and harm, it depends on how you choose to use it. You can also choose not to use it at all, drop the things that are making you feel impure, and let time do the rest. The basic thing is that you understand what you are doing, and do everything with full and conscious awareness
And also drop this guilt within you about having used the substances in the past. You didn't know what you were doing, so you made some mistakes, we all make them, now that you understand simply don't repeat the same mistakes, learn from them, and move on. But there's no need to feel guilty about those years of drug use, as some bad or evil thing... if using drugs makes you feel bad and brings your consciousness down, then just simply stop using. Everything else will settle with time (your system will clean out its toxins, and you will return to your fresh, and normal, natural state)