Star Trek: The Next Generation Season 1 Episode 22

Wesley: Data, I can understand how this would happen to the Ornarans. What I can't understand is why anyone would voluntarily become dependent on a chemical substance.
Data: Drug addiction is a recurring theme in many cultures. However--neither being human nor having had any comparable experience, firsthand or otherwise--I am afraid I cannot give precisely the answer you seem to hope for.
Tasha: I believe I can, Wesley. First of all, nobody ever wants to become dependent; that happens later.
Wesley: Still, if people know it happens, why do they start?
Tasha: Remember what I told you about life on my home planet? There was so much poverty and violence that, for some, the only escape was through drugs.
Wesley: Escape? How does a chemical substance provide an escape?
Tasha: It can't really. But it makes you think it is. It's difficult to explain, but drugs can make you feel...good. They put you on top of the world; you're happy, you feel in control of everything and everybody.
Wesley: But what's the point, if you know it's artificial?
Tasha: Because it doesn't feel artificial until the drug wears off. Then you feel just the opposite of what you did before: sad, powerless, hopeless, in pain...And the worst part is, the more often you take the drug, the more your body adapts to it--so that you need higher and higher doses to get back the good feeling. However, those larger doses also leave you feeling worse--and for longer--after it wears off. That's how you get trapped. Before you know it, you're not even taking the drug to feel good anymore; you're just taking it to keep from feeling bad. At that point, all you care about is getting your next dose. Nothing and nobody else matters.
Wesley: I see how it works, Tasha, but I'm afraid I still don't understand it. Sorry.
Tasha: Wesley, don't be. In fact, let's hope for your sake you never do.