When saying things like this, I think you should intuitively consider the corollary of your sentence. If people are using drugs to "escape from reality" presumably because have insufficient money to do nicer things, then the implication is that people who have lots of money would use drugs at a substantially lower rate.

And so this is pretty easy to test. I did a quick search for 'marijuana use by rate by income' and the first paper that I came upon [1] showed there is indeed quite a strong correlation between substance use and socioeconomic status - in other words, the richer or more privileged individuals were (in terms of coming from wealthy family backgrounds), the more likely they were to use drugs.

So unless there is some confounding variable that we may not be considering, it seems fairly easy to reject the hypothesis that people are using drugs because of a lack of money.

[1] - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3410945/