There's a wide variety of drugs of abuse: LSD, Anthrax (this is also a very good thrash metal band, another drug of abuse), marihuana, crack, Casimiro's smile... Depending on your neighborhood, your friends and a lot of many others factors, you'll see some of this drugs; being the marihuana the one that, personally, I've seen the most.

Despite I've had the chance of trying marihuana, I've always declined it. I don't know, it's just part of me and my values. In fact, I guess that the hardest drug that I've ever tried has been the salbutamol, it was a very extreme experience; I almost fell into a coma.
If you see the image on the left side, you'll appreciate how an innocent baby is becoming addict to salbutamol consumption; notice that he's trying to fight against this evil woman but all his attempts are futile. By her side, she's smiling because she's enjoying the baby's suffering and she knows that in the future he'll be another victim of one of the most powerful legal drugs of abuse (and he probably die during his adolescence before knowing the love of his life because the illness that salbutamol induces: asthma).
I have a friend who's addicted to marihuana. The most of the time he have his eyes red and "chinese-like" and while he is flying around Saturn, he's always saying non-sense things. But he's funny, I guess. I remember once that he wanted to left this drug, but after a time he said that he NEEDED that drug... researching, I found that this phenomenon it's called the withdrawal syndrome.
Depending on the drug, you'll see different effects: you'll be lazy or you could be more active, happier or sadder... Depends on which drug you like the most (some friends have told me this).
I think that, as a pharmacist, my responsibility is to teach the people which drug is "good" and which is "bad" to avoid the self-medication and with this I can fight the abuse of some drugs, including the drugs of abuse, because I'll have the tools (I hope) to buy fight'em.