I haven't read the study and as it's 2 in the morning I'm not likely to at the moment, but it seems more likely to me that they get some data on overall hospitalizations in which Drug X is a factor, as well as data on fiscal damage, crimes committed (I needed to rob that lady to buy some crack) and so on, then collate it.
This is especially likely for the 'social damage' aspect - think drunk and disorderly, drink driving, alcohol fueled fights, etc. These figures could then be compared against the numbers of people overall who use the drugs, potentially mitigating (at least partly) the over-representation of alcohol use in the population. Though, I'm not a statistician.
It would be a completely meaningless study if it was the example cited above. However, I do think it's largely known that alcohol destroys lives in much the same way as a bunch of other drugs, destroys health, and leads to notoriously bad decision making which can have dramatic flow on consequences.