Shit happens, but some folks are just begging for it. I'm sure a normal dose of, say, L, couldn't do that to a normal guy.
Depends. Most drugs affect the application layer of what makes you.... you. They make small changes that go away when rebooted. Pot and alcohol fall in this category.
A few affect the operating system that the thing called "you" runs on. They make more substantive changes in how you act and change a number of things that make you you. Good opiates fall in this category.
LSD and such twiddle around with your firmware or in some cases your microcode. They can change who you *are*, and can rewrite the thing your mental operating system runs on. Use with care.
I don't know anything about opiates (don't care for addictive substances or anything that you could die from), but what LSD does is create new neurons as well as new connections between neurons (which is why some experience synesthesia under the influence).
It's pretty much what happens when you learn new things and also why it's so powerful in treating depression by breaking up bad habits (or thought patterns) through the creation of new ones.
This can go out of control if you take retarded amounts in retarded environments and situations, but responsibly (low dose, no mental issues, physically and mentally healthy, not on medication, no combination with other drugs etc.) this isn't just harmless but can also be a very useful tool.
One time I used small doses to study and the results were pretty remarkable. You can go much deeper than you ever could hope to in a sober state, although it's very easy to "overdose" in the sense that you'd be too busy staring at random stuff and going off on tangents instead of focusing on your task.
Speaking of dips, eating a snack just made me extremely hungry. Thanks body.
Holy fucking volatility Jesus.