Unfortunately, the word "drug" is incredibly broad and general. Nicotine and caffeine are "drugs" and they increase cognitive functioning as well as sharpening focus and clarity. Definition is important, because ibuprofen is a drug. Or are we talking about anything that influences the mind? Everything influences the mind, not just the chemicals we breathe or eat on purpose.
To paraphrase XKCD, we are basically bags of chemicals that ingest other chemicals to survive. Certain chemicals influence the brain to increase focus, certain chemicals make perception cloudy, certain chemicals make you sleepy (as in, when you eat too much and your brain secretes a chemical that makes you want to sleep), and certain chemicals make you die (like cyanide, or too much H2O, or even too much oxygen). But I thought oxygen was a good thing?? It's myriad cause and effect, everything conditioned.
I've seen a lot of people who dont use any "drugs" who are plain idiots or selfish, etc., and i've seen a lot of people who do
use certain "drugs" and they are loving, intelligent, insightful. It goes either way. The point is in how someone responds to the conditions that are present.
Everything we do alters our minds, watching Jerry Springer is not conducive to a life of insight and calm.
So, im not promoting it, but im not denying it either. Let's look at the whole picture. Nonetheless, The Vinaya is clear in that any behavior that causes mental and physical inertia or too much passion is to be fully avoided; same as avoiding rajasic and tamasic foods and activities in yoga.
So, though its pretty clear that we should avoid things that cause excess inertia and passion, the whole "intoxicants that cause heedlessness" isn't all that straightforward. We're talking semantics here and plenty of people have different opinions on what causes mental clarity or fogginess. Like cocaine or speed, is that mental clarity or just a very sharp delusion?
The recorded teachings that we assume are the words of the Buddha are teachings directed at certain individuals and teachings directed at the masses. IMO, these are not necessarily absolute teachings. While obviously, an intelligent and aware person has the capacity to decided whether it's safe to go through a redlight they've been stopped at for 2 minutes in the middle of nowhere at 2am, many members of the general populace are not. This is why we have certain laws.
So, we can give you a clear answer in regards to what is doctrinally recorded about taking intoxicants, but your deeper answer in regards to reality itself wont come from anyone outside. Just be prudent and aware in whatever you do, though, dont necessarily discount any particular teachings either. With wholesome intentions, I feel like you will lead yourself in the right direction. But no drug will reveal truth in and of itself, thats why the Buddha also taught us to be "an island" and not be dependent on our environment. Realization doesn't come from anything outside of ourselves or by adding anything "extra" to the mix.
You know "be a lamp unto yourselves" and whatnot.
Sorry for the long answer, hope I made myself clear