Seems like a strange statistic - high school encompasses only 4 years of a person's life, whereas there's no (practical) limit on when someone can be an addict.
Using a number like 25000 is difficult to understand in your head.
4 years is a lot of time!
You probably see or are aware of high school age individuals throughout your day-to-day.
Now imagine for every 1 high school age young-adult, your city also has 1.5 injection drug addicts.
I think that puts things in perspective pretty well.