Although CNN is claiming that pill is use outpacing marijuana amongst college kids, its sources are problematic. The major national surveys-- which, although not perfect, are considered the best sources of data on drug trends-- do not find that more college students use prescription drugs than marijuana.
Monitoring the Future is the national survey done by the University of Michigan for the National Institute on Drug Abuse. Its most recent report finds that 49% of college students report having tried marijuana-- while just 26.6% have used any other drug illegally. If we look at specific prescription medications, the numbers are significantly lower. For example, 12.3% have taken amphetamine (usually prescribed for attention-deficit disorder) recreationally; 14.4% have misused prescription pain medications.
If we look at recent use, the numbers are the same: 19.5% have smoked marijuana in the last 30 days, but just 3.1% have misused prescription pain medication and 2.9% have misused amphetamines.
While CNN's source Joe Califano says he "wouldn't be surprised if right now at this point in time, there are more kids abusing prescription drugs than abusing marijuana,"-- actual drug researchers would be. The data just doesn't support that contention. Califano heads Columbia's National Center on Addiction and Substance Abuse, which is notorious for its misuse of statistics.
Similarly, while CNN claims that prescription drug misuse is especially common in the middle class, this is also not borne out by the data. Young adults who don't attend college (and are thus less likely to be middle class) are more likely to misuse prescription drugs than those who do go to university, according to the same national data.
While some prescription drug use has been increasing (and other use is down) amongst college students, it has a long, long way to go if it's going to catch up with marijuana, something that has never been seen even when prescription drug use rates were extremely high in the early 80's.