Sadly, I tend to think it's the other way around. Most songs that sounds like they are about drugs actually ARE about drugs, I more often have the problem I miss out on the message, or realise many songs I loved growing up I never really knew were about drugs.
The thing is, a song about drugs is not gonna spell it right out. For one thing I thing that's illegal, anyway, or at least has been for the most of history as it would be considered as triggering and bad advertising. So it's not gonna be like that. Songs about drugs are written in metaphors or double meanings, and could be explained to be about something else if asked (and usually is in a humorous sort of way). It's just that if the song is NOT about drugs and to be taken at straight face value there would be no real meaning or coolness to the song, and no audience that would really be able to relate much to it. It'll just be something that sounds cool, catchy as fuck, and kind of mysterious (which are most popular songs anyway).
One problem is that growing up the people who make the music you're listening to are gonna be much older than you, and have much more information and experience, many of them may have been all the way round the block drug-wise. And that's why it's such a strong subject for them. But most people, apart from those older and wiser, or other members of the music- or drug-scene aren't gonna get what it's about. Like I said, it's not legal, or at least seen as moral.
But a ridiculous amount of rock-stars have been drug-addicts. Many of those mentioned in this thread have the classic drug-addict look (and it can show). Drugs are insanely common in the music scene, and hard to resist when they're offered someone for free by people wanting to become their friend all the time. But once true addiction starts, they have to get hold of it for themselves, as it's embarressing for someone who's supposed to be a rich rock-star to go around begging for drugs all the time. The also get problems with upholding their work-duties and it eventually gets as bad as for everybody else (plus having to hide it or become famous for it).
I am actually amazed at the amount of popular culture that is really about drugs that most people don't realize. Often things made by older people. Stories like "Peter Pan" and "Alice in Wonderland". A lot of it are clever references to tdrugs they used when young, which are going to resonate with people who get it and make it more popular. I'm guessing that's why it's so popular - to make more money on it.
I remember once seeing an older chemist in his 60s talk on TV and being asked if the plant Nightshade gave an high. An he kind of laughed and said "Yes, but it's a very coarse high" in a kind of double meaning ("A coarse high" meaning "A dirty high" - which I thought sounded impressively scientific at the time, and he seemed respectable, but the expression "A dirty high" is a common term in the drug world). And they were probably counting on older people in the know getting what he was on about.
I think it's a sort of unspoken understanding kind of thing. They know it can't be prooved and can easily be explained away because people are too stupid, but at the same time, those in the know will know what it's about and take to it. You just need to spend some time in this world to see that's how it's usually done.
