I did a lot of drugs in my youth (ages 19-maybe 25?). I was pretty catholic in my drug tastes too: drugs I took included marijuana, cocaine, speed (meth), LSD, mushrooms, laughing gas, opium, various prescription drugs used recreationally (vicodin, percocet, and codeine among others), and some more unusual ones like dextromethorphan (a primary ingredient in cough syrup), hallucinogenic cactus, and morning glory seeds. Of course I drank alcohol and tried cigarette smoking (briefly; I didn't want to get addicted). In fact, the only popular drugs I didn't try were heroin (although the opiates are basically the same chemically) and Ecstasy.
And you know what? I really enjoyed it. Taking drugs provided me with all sorts of positive and interesting experiences. I never developed any kind of addiction problem, never did anything I really regret, and never ran into any serious trouble. If drugs were legal, I would probably still do them (assuming childcare was lined up). I particularly regret that LSD is not legal, because I found its effects so interesting. (It also is not addictive and does not cause any physiological problems: American drug policy is not at all rational.)
This is something that people tend to ignore when discussing the "drug problem": drugs are a lot of fun. That's why people do them in the first place! They are fun because they reduce your inhibitions; allow you to perceive the world in another way; give you a break from your own psyche; and affect your mood positively. Many other things usually approved of by society do the same thing (running, breastfeeding, meditation, traveling, even eating): drugs are just quicker and more efficient.
I consider drugs and alcohol, caffeine, and tobacco as one and the same (the only reason they are not always classed together is an artifact of our stupid drug policy). Alcohol, caffeine and tobacco are drugs, and the reasons to use it are exactly the same ones for using opiates (heroin, vicodin, etc.) or amphetamines (meth, etc.). There is no (mental, moral, physical) difference between having a couple of drinks after dinner; smoking a joint; popping a few pain pills; snorting a line of coke; or having a cigarette. The effects of the drug might be different (like whether you become sleepy or energized, or aggressive or affectionate), but that is all.
Some people do develop addiction problems (and some substances are more addictive than others: why I was always very careful with tobacco). But in my opinion, addiction has very little to do with the actual drug. Addicts probably have some sort of genetic predisposition to addiction.
However, having known a lot of addicts (both in my family and in my drug-taking days), I believe psychological factors are the key to addiction. I have never met an addict (as opposed to a recreational user) who didn't have: 1. significant mental health problems (prior to the addiction); 2. a dysfunctional family (usually pretty severely dysfunctional, and the more dysfunctional, the worse their addiction was); or 3. at least one, and usually more, seriously traumatic experiences in childhood/youth (rape, witnessing significant violence). Actually most of them had at least two of these factors.
I read Katie Granju's blog, which I enjoy, but I find her posts about her son's addiction (he died of a drug overdose about a year ago) seriously annoying. She has frequently referred to his addiction as "a disease", but the reality is, addiction is not a disease that just descends out of a clear sky and "could affect anyone".
People are addicts because they are in intolerable emotional, psychological or psychic pain, and drugs give them a release from it. There is no other reason, for her son (Henry Granju), or anyone else. The fact that she has not addressed this, focusing instead on drug supply issues, is both troubling and socially damaging. (Henry, like many addicts, wanted the experience of being high rather than a particular drug, and took whatever drugs were available in pursuit of this: I have seen many other addicts just turn to alcohol if street drugs weren't procurable.) If she really wants to help other troubled youth, she should advocate for decent mental health services (not available for most, especially if you are poor), preventing child abuse and crime, and providing parents with the necessary resources (psychological, financial and physical) to do a decent job.