It’s not unusual for a drug shortage to last more than a year, but there’s usually a pretty clear reason. The Adderall shortage, meanwhile—which hit the one-year mark last week—remains a mystery. The U.S. Food and Drug Administration (FDA) has shared little information with the millions of Americans who have struggled to access the common ADHD treatment. Experts who have spent their careers studying shortages are “baffled.”

As it turns out, there might not be a single person who actually knows what’s causing the Adderall shortage. Lawmakers say that’s because the three parties that work together to get the medication bottled and sold aren’t required to communicate enough with one another—and nobody wants to accept the blame. Here’s who’s involved:

• The U.S. Drug Enforcement Administration (DEA). Because amphetamine salts, which are the active ingredient in Adderall, are controlled substances, the agency sets an annual cap on how much manufacturers can use. Even though the DEA has to share this quota publicly, it doesn’t have to disclose any information about how the total is split among manufacturers. And by the way: 30% of last year’s quota never made it to the public.
• The FDA. The FDA helps the DEA set its annual quota, and it also determines the regulations for how Adderall can be manufactured and sold. The agency has the power to enforce movement on shortages, but only to a point. Right now, the FDA has joined the DEA in blaming manufacturers for delays, citing the allotment that never made it to market.
• Drug companies. Pharmaceutical companies are required to inform the FDA about medication shortages, but they don’t have to provide detailed information about the cause. Manufacturers have mainly blamed increased prescription rates for the shortage, but there’s really no way to know for sure what’s going on.