Any one who has studied psych, sociology or any other field that looks at studies and experiments knows that a lot of the information presented can easily be biased. The way information can be presented can be very deceiving to prove a point of the experimenters.
Okay, say most of western culture is on a drug, perhaps caffeine is one of those drugs. Billions of people consume it. Cough medicine, pot, coke, anti depression, anxiety, headache medicine, nicotine etc. There are too many "drugs" that are consumed and this study MAY try to imply the use of drugs to allude to mind altering drugs to give the reader a false representation in order to prove a point.
So the inclusion of drugs that are legal and illegal get lumped together. It can be 60% only use legal, 10% use only illegal and 30% use both.
Plus, the use of certain words delivers a persuasive attitude. "Most of western society is drugged up." That sounds really negative. Perhaps if worded, "most of western society has an elevated use of pharmaceuticals as well as other drugs..." But than again, the word drugs alone carries such a strong impact that the word itself is jaded.
It's like saying that child is autistic. "autistic" carries a more negative, and labeled connotation compared to "that child suffers autism."
The study did actually indicate which percentage was legal, and which was illegal. It didn't use caffeine as a drug. But it did use pain killers, opiates, and anti-depressants (which are all just as dangerous as illegal drugs).