Medicines to treat attention deficit hyperactivity disorder are in such short supply that hundreds of patients complain daily to the Food and Drug Administration (FDA) that they are unable to find a pharmacy with enough pills to fill their prescriptions. The shortages are a result of a troubled partnership between drug manufacturers and the Drug Enforcement Administration (DEA), with companies trying to maximize their profits and drug-enforcement agents trying to minimize abuse by people. Shortages, particularly of cheaper generics, have become so endemic that some patients say they worry almost constantly about availability. The DEA sets manufacturing quotas that are designed to control supplies and thwart abuse. Every year, the DEA ... allots portions of the expected demand to various companies. How each manufacturer divides its quota among its own ADHD medicines - preparing some as high-priced brands and others as cheaper generics - is left up to the company. Officials at the FDA say the shortages are a result of overly strict quotas set by the DEA, which, for its part, questions whether there really are shortages or whether manufacturers are simply choosing to make more of the expensive pills than the generics, creating supply and demand imbalances.