The largest is marijuana. Here's the chart:
The only users I'm concerned about are the habitual users (past 30 days), and that's been flat for 15 years at 5%, and down significantly since 1979.
One more for comparison, cocaine, the #2 illegal drug:
Habitual users (past 30 days) is 0.7%, down from 3.0% in 1985. Hallucinogens at #3 add another 0.6%. These are not big numbers.
But that's not my point. My point is that drug users do not "suffer the consequences" today, nor will they if drugs are legalized. Drug users cost me money for everything from their hospitalization costs to court-appointed rehab. From stealing to feed a habit, to lost productivity and accidents on the job.
We live in a cradle-to-grave nanny state. Legalization would just add to the existing burden.
Now, if we first get rid of the nanny state today, then the author might have a point when saying that drug users would "suffer the consequences". But we haven't and he can't.