Shortages of medicines like Ritalin and Adderall are so endemic that some patients say they worry almost constantly about availability.

Drugs to treat attention deficit hyperactivity disorder are in such short supply that hundreds of patients complain daily to the Food and Drug Administration 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, with companies trying to maximize their profits and drug enforcement agents trying to minimize abuse by people, many of them college students, who use the medications to get high or to stay up all night.

Caught in between are millions of children and adults who rely on the pills to help them stay focused and calm. Shortages, particularly of cheaper generics, have become so endemic that some patients say they worry almost constantly about availability.

While the Food and Drug Administration monitors the safety and supply of the drugs, which are sold both as generics and under brand names like Ritalin and Adderall, the Drug Enforcement Administration sets manufacturing quotas that are designed to control supplies and thwart abuse.

Every year, the D.E.A. accepts applications from manufacturers to make the drugs, analyzes how much was sold the previous year and then allots portions of the expected demand to various companies.

How each manufacturer divides its quota among its own A.D.H.D. medicines — preparing some as high-priced brands and others as cheaper generics — is left up to the company.

Now, multiple manufacturers have announced that their medicines are in short supply. The F.D.A. has included these pills on its official shortages list, as has the American Society of Health-System Pharmacists, which tracks the problem for hospitals.

And the American Academy of Child and Adolescent Psychiatry has told the more than 8,000 doctors in its membership that shortages seem to be “widespread across a number of states” and are “devastating” for children.

Officials at the Food and Drug Administration say the shortages are a result of overly strict quotas set by the Drug Enforcement Administration, 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.

The situation has made for a rare open disagreement between two federal agencies.

“We have reached out to the D.E.A. and told them that there are shortage issues,” said Valerie Jensen, associate director of the F.D.A.’s drug shortage program. “But the quota issues are outside of our area of responsibility.”

Still, Special Agent Gary Boggs of the Drug Enforcement Administration’s Office of Diversion Control, said in an interview, “We believe there is plenty of supply.”

Some high-priced pills are indeed readily available, and D.E.A. officials said that so long as that is the case, they believe that A.D.H.D. drug supplies are adequate. Agent Boggs attributed any supply disruptions to decisions made by manufacturers.

Company ‘working diligently’
Novartis, for instance, makes both branded and generic versions of Ritalin; Shire Pharmaceuticals does the same for Adderall XR. In both cases, the companies have ensured that supplies of branded drugs are adequate while allowing generic versions to go wanting.

“We are working diligently to ensure our supply of these products meets demand, including discussions with D.E.A. regarding our quota levels for these controlled substances,” said Kathy Bloomgarden, a spokeswoman for Novartis.

But those who rely on the drugs can react very differently to apparently similar medicines, so an adequate supply of one drug does them no good when their preferred medicine is unavailable, patients and their doctors say. And prices can vary so much that some patients say they cannot afford to switch.

Lynn Whitton of Westport, Conn., who has an attention deficit hyperactivity disorder, expressed disbelief when told that the Drug Enforcement Administration said there were no shortages of A.D.H.D. medicines. “What?” she said. “I’m just flabbergasted!”

Ms. Whitton said she had recently gone to more than a dozen pharmacies in Westport and New York City before finding one that would partially fill Ritalin prescriptions for her and her 18-year-old son, who also has the disorder.

Erin Fox, manager of the drug information service at the University of Utah, said problems arise when there is a mismatch between what manufacturers choose to make and what patients are prescribed.

And, Dr. Fox said, while manufacturers sometimes use their limited quotas to ensure adequate supplies of high-priced branded drugs at the expense of low-profit generics, all of the issues would be resolved if the Drug Enforcement Administration were simply more generous with its quotas, particularly since sales of A.D.H.D. medicines have risen so rapidly.

Likened to cocaine high
Doctors wrote 51.5 million prescriptions for A.D.H.D. drugs in 2010, with a total sales value of $7.42 billion — an increase of 83 percent from the $4.05 billion sold in 2006, according to IMS Health, a drug information company.

Agent Boggs of the Drug Enforcement Administration said his agency was concerned that A.D.H.D. drug abuse was on the rise. “We see people abuse it in college and then continue to abuse it nonmedically once they leave,” he said.

Since the drugs have been shown to improve concentration, and not just in people with A.D.H.D., they have become popular among students who are seeking a study aid. And since they can impart a euphoria that users have likened to a cocaine high, the pills are sometimes ground up by people who snort them for a thrill.

On the other hand, there are people like Sheryl Greenfield of Bryn Mawr, Pa., an A.D.H.D. patient who spent days calling dozens of pharmacies to find a generic substitute for Adderall XR. She finally gave up and bought the brand, and her co-pay went to $200 from $10. “I can afford the difference, but I know some people who can’t,” she said.

Shortages of amphetamine-based drugs like Adderall became so endemic that many doctors switched patients to methylphenidate-based drugs like Ritalin, creating shortages among those medicines as well, according to the F.D.A.

Ruth Hughes, chief executive of Children and Adults with Attention Deficit Hyperactivity Disorder, a patient advocacy organization, said the drug shortages had become so acute that many patients were going untreated, increasing their risks of deadly traffic accidents and job dismissals. “The consequences of not getting treatment can be devastating,” Ms. Hughes said.

Dr. Alexander Lerman, a psychiatrist from Chappaqua, N.Y., said his patients could not simply switch from one medicine or dosage to another without consequences. And some of his patients, he said, cannot afford the branded version of the drugs.

“For the first time in my career,” Dr. Lerman said, “there is this enormous and mysterious scarcity of the basic product that is proven to work.”