Millions of Americans rely on drugs like Adderall and Ritalin to treat Attention Deficit Hyperactivity Disorder (ADHD). But it's reportedly getting hard for many patients to find pharmacies with enough pills in stock to fill their prescriptions. That could mean inattentiveness and disruptive behavior from children at school, and adults struggling to concentrate at work. What's behind the "worrisome" drug shortage? Here's what you should know:

How bad is the shortage?
Demand for Adderall is reaching "all-time highs," says Toni Clarke at Reuters. In 2010, more than 18 million Adderall prescriptions were written, a 13.4 percent increase from 2009. And the supply can't keep pace with that demand. The Food and Drug Administration (FDA) receives hundreds of complaints each day from parents unable to find the drugs for their kids, and has added these medications to its "official shortages list."

What's behind the shortage?
Many are blaming the Drug Enforcement Administration (DEA), says Gardiner Harris at The New York Times, which sets strict quotas to curb abuse. (College students, for instance, are known to illegally take the drugs as study aids.) In a "rare open disagreement," the FDA has swatted at the DEA, blaming the latter for the shortage. For its part, the DEA blames drug manufacturers, who are electing to make more expensive brand-name pills and fewer generics, thus "creating supply and demand imbalances," Harris says. Indeed, "shortages, particularly of cheaper generics, have become so endemic that some people say they worry almost constantly about availability."

How can patients cope?
Not easily. High-priced drugs are more readily available, but many Americans can't afford them. Sometimes, the price difference is hundreds of dollars. And manufacturers have been known to distribute "too much product in one place," says JoNel Aleccia at MSNBC, which means long trips for those looking to fill their prescriptions. "For people with ADHD, there's already a stigma attached to it," one patient tells MSNBC. "You end up feeling like you're drug-seeking. It doesn’t make you feel good."

Sources: MSNBC, New York Times, Reuters