From an earlier article referenced by this article:
Drugmakers and the Drug Enforcement Administration, which regulates controlled substances, are pointing fingers at one another for the problem, said Erin Fox, senior pharmacy director at the University of Utah Health.
Makers of ADHD drugs say they don’t have enough ingredients to make the drugs and need permission from the DEA to make more. The DEA is insisting that drugmakers have not met their quota for production and could make more of the drugs if they wanted. Adderall is a controlled substance regulated by DEA, which sets limits on how much of the active ingredient drugmakers are allowed to produce in a given time frame. Drugmakers must get approval from the DEA before they go over their quotas.